Most Indo-European languages have multiple tenses, to differentiate things that have happened from things that are happening right now from things that will happen, plus some to define what had happened before that, not to mention some that are a bit less identifiable in their everyday uses (we doubt that most people have understood the Pluperfect Subjunctive). It mostly works fine when your timeline is a strict progression from cause to effect.
Unfortunately, when you are watching the San Dimas Time, winding through the threads of the Timey-Wimey Ball, chasing another time traveler who is always one step ahead of you, it can become awkward. As a result, time travelers will often stumble over their wording, leading to use of tenses that can be torturous to understand.
Usually this is an experienced traveler explaining in eloquent yet incomprehensible terms that they didn't "just succeed", when you return from an adventure in the future. Alternatively, a less experienced character will attempt to explain what's going on, and struggle with their terms.
If your Future Me shows up, there may be pronoun trouble on a similar style, especially if there's several versions of future characters knocking around.
This is related to Meanwhile, in the Future, Anachronic Order.
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Mikuru from Suzumiya Haruhi is aware of the tense trouble, but she keeps flubbing it anyway. Considering that Mikuru is spacey and Moe Moe, this leads to Adult!Mikuru showing Kyon a mole on her breasts while saying something like "But you were the one who told me about it...wait, has that not happened yet? oops...". Later in that episode Kyon casually asks Mikuru if she has a mole "right about here" and points to the location on his own chest. She turns around, checks, and starts trying to beat the information out of him. That would be where Kyon "told her about it"- it's a paradox.
In Time Agent the objective is to have always been winning by using time travel to have changed the past, while never having had time travel invented. The flow of causality operates according to the Schrödinger's Gun trope, which means that technologies often work until you discover that even before you had been making changes to the timeline, they had never been working. In one instance the player commander of the Zytal had to leave and be replaced by another player, but from the board's perspective, the new player had always been the commander of the Zytal, for the previous commander had never been playing.
MAKE IT STOP
In Watchmen, Dr. Manhattan, who is able to perceive the past, present and future, says "Yes, yes, he killed Blake and half of New York. Excuse me, Rorschach, I'm informing Laurie 90 seconds ago," to Laurie "Silk Spectre" Juspeczyk, being confused by tachyon interference, before saying the same thing to Rorschach 90 seconds later. He's even in the exact same pose and position (relative to the walls of the panel) both times he says it. Also, the whole flashback (flashnow?) scene on Mars.
In an Uncle Scrooge story, the evil witch, Magica has this problem
Magica: This is like all the times in the past that Scrooge himself has chased me in the future. I mean... what am I talking about?
A frequent out-of-universe problem when trying to describe events crossing Crisis on Infinite Earths, due to the major differences in how the retcon affected different characters and different past events. A few characters were rebooted as completely new characters (Wonder Woman), some were made so that they had been around before the Crisis, but their personalities and histories suddenly had always been very different from what all previous comics portrayed (Superman), and some had basically the same history and memory that they had had before the Crisis (The Flash, Green Lantern). Therefore, there's both the reader's perception of what "Pre-Crisis" and "Post-Crisis" means (Pre-Crisis: Silver- and Bronze Age, Post-Crisis: Dark- and Modern Age), and there's the characters' perception of what "Pre Crisis" and "Post Crisis" means (basically: Pre Crisis: Before Barry died, Post Crisis: after Barry died). This leads to descriptions like "After the Crisis, Batman changed so that he had been dark and brooding both before and after Barry died."
Also, Barry's life, career and friendship with other characters, as well as the vague event note from the characters' point of view: that Really Big Deal that no one really remembers but no one ever wonders about that caused his death, are all perfectly compatible (as far as their memories are concerned) with their personal histories and timelines that had been established after the Crisis was written. So basically, the characters can all recall and talk about events that as far as they are concerned, occurred when Barry Allen was still alive, but most of those events are significantly different from how they were reported by comic books written before the Crisis was published.
The Invisibles sometimes shows events taking place outside of time, where not only tenses suffer but the entire linear construction of sentences. One such nonlinear word balloon might contain the words "From" "look" "at" "you" "are" "in" and "allnow", to be arranged by the reader in whatever order they need.
Sanji: Hell if I know. Maybe Robin does. Did. Would... Will? Damn.
In Equestria: A History Revealed, the narrator's confusing take on time travel and method for dealing with the Starswirl inconsistency tends to invoke this trope more than a few times.
Harry Potter and the Methods of Rationality has this gem, which is more to do with Time Travel Pronoun Trouble: '"If I and my future self interact, we'll still see the same thing as both of me, even though, on my first run through, my future self is already acting in full knowledge of things that, from my own perspective, haven't happened yet..." Harry's voice trailed off into the inadequacy of English.'
The Twilight Child: Comes up during one chapter, when there's two different Twilight Sparkles, one from "now", and one from next Tuesday, who are being watched from a character for whom they are both Past-Twilight. The character's attempt to keep everything straight in her head fails, and on more than one occasion the narration just gives up trying to make sense of it.
The tagliney prophecy which drives the action of the animated Science Fiction film Light Years makes use of it: "In a thousand years, Gandahar was destroyed. A thousand years ago, Gandahar will be saved."
The telepathic mutants who recall this prophecy are acutely aware of the past and the future, to the point where their language has no present-tense verbs, and instead use past- and future-tense verbs simultaneously. Example; instead of telling the hero "I am your friend," a mutant says "I was/will be your friend."
Gordon: We've found his next target. He's put it in tomorrow's newspaper. Kevin: Then we'd have been too late. If only there will be something we could do.
In Groundhog Day, Phil never really has to worry about his tenses because he's the only one who realises he's in a "Groundhog Day" Loop, but that just makes some of what he says funnier for the audience.
Phil: [After being told something will be handled tomorrow] Well what if there is no tomorrow? There wasn't one today!
Mostly avoided in Looper, but there are a few phrases here and there that cause tense trouble.
Joe: In seventy years, time travel will have been invented.
Inverted in Flight of the Navigator, when David gets asked by the police what year he thinks it is, unaware he's gone 8 years into the future.
In Harry Potter, Hermione insists on the correct tense when she travels back in time. Hermione likes things just right!
The Hitchhiker's Guide to the Galaxy has a good excerpt on the mechanics of time travel useful for this. There's even a book written In-Universe in The Restaurant at the End of the Universe called the Time Traveler's Handbook of 1001 Tense Formations by Dr. Dan Streetmentioner. However, the book has been described as "an exceptionally dull read", and most readers only get as far as the section on the Future Semiconditionally Modified Subinverted Subjunctive Intentional before giving up. Because of this, in later editions of the book all pages beyond this point have been left blank to save on printing costs, which will turn out to be... uh, is going to be discovered to have been... no, is probably, at some point, sooner, later or before, going to be Hilarious in Hindsight... or something...
Note that the titular Guide doesn't even bother trying to explain the tenses, and simply notes that it does not use the future perfect tense, because it was discovered not to be.
One example of tense from the Handbook is "wioll haven be," apparently a conjugation of "is."
There is also an excerpt from Mostly Harmless that goes (and try to wrap your mind around this one, now): Anything that happens, happens. Anything that, in happening, causes something else to happen, causes something else to happen. Anything that, in happening, causes itself to happen again, happens again. It doesn't necessarily do it in chronological order though.
There is an example paragraph (describing the process by which one can visit Milliways, without first making a reservation or arranging payment, then do both those things once you return to your home time). Each sentence is significantly more weird then the one before, from two-word combinations in the first to the last sentence being entirely composed of time-travel-tense-altered words.
In Equal Rites, when it is explained that the dead are unbound from all dimensions, the narrator describes the fact that a cat appears to simultaneously be its own age, a newborn kitten, and a decrepit moggy, as resembling a kind of white, cat-shaped carrot, "which will have to suffice until someone is able to devise effective fourth-dimensional adjectives".
And at the end of all stories Azrael, who knew the secret, thought: I REMEMBER WHEN ALL THIS WILL BE AGAIN.#
In The Last Continent, Scrappy tries to explain to Rincewind that he knows Rinso can save FourEcks because he's already done it, but he can't just go home because he hasn't already done it yet.
Averted in Poul Anderson's Time Patrol stories. In those stories, the Patrol developed an artificial language, called Temporal, which allowed Patrolmen to discuss such matters without any of the tense problems raised in this trope. Since only Time Patrolmen learned and used Temporal, it also served as a way that Patrolmen could speak between themselves without risk of being overheard (or more accurately, understood) by others.
Larry Niven's stories involving Svetz love to play with this trope. Svetz's solution to a time paradox involving the destruction of Ford's Model-T demonstrates very well how bad English is with time travel:
Svetz: Maybe we can go around you. Zeera, try this. Send me back to an hour before the earlier Zeera arrives. Ford's automobile won't have disappeared yet. I'll duplicate it, duplicate the duplicate, take the reversed duplicate and the original past you in the big extension cage. That leaves you to destroy the duplicate instead of the original. I reappear after you've gone, leave the original automobile for Ford, and come back here with the reversed duplicate. How's that? Zeera: It sounded great. Would you mind going through it again? Svetz: "Let's see. I go back to—
In Paradox in Oz by Edward Einhorn (1999), Ozma travels in time with the assistance of a Parrot-Ox, and finds out that there are two kinds of time she can travel in: "Oz time" and "Ozma time", the former being travel through the timeline of the entire land of Oz, while the latter is travel within her own personal timeline (letting her undo things she did, including other time-traveling).
The Narnia Time in effect between the territories in The Pendragon Adventure occasionally causes this sort of trouble. Usually involving rookie Travelers (We're looking at you, Spader and Siry).
"There's an old windmill up there. It was some kind of look-out post during the war. Is, I mean."
In the Gospel of John in The Bible, Jesus says, "Before Abraham was born, I am!" This is a statement of divinity — "I am" is connected to the "name" Yahweh or Jehovah, as God told Moses ("I am that I am") — instead of evidence for a time-travelling Jesusmobile, but tenses for the omnipresent seem to run into the same problems with language.
The Bible also tends to record prophesies as though the future events they describe have already happened.
In the Young Wizards series itself, it's mentioned in passing that the Speech, the Language of Magic with which reality was written, does have the words to deal with thing like this, including talking about something in the past which used to be but no longer is due to the past having been changed.
In the Book of Night with Moon Arhu, a visionary, says, " Au, Rhiow, the way we talk about time doesn't work for talking about vision. I need new words or something!" Presumably he has not learned enough of the Speech yet.
Referenced in a Star Trek Expanded Universe novel about the Department of Temporal Investigations, which deals heavily with the logic and philosophy behind this trope. It concludes that the simplest solution is to look at things from the perspective of someone outside time and pretend everything is happening at once, and as such simply use present tense for everything.
Time Scout makes this easy. It's running on a lot of different San Dimas Timeportals to the past. If a portal leads to 1888 and the time travellers are talking about an event in 1889, they use the future tense. When they're talking about the future/present, they just use the present tense.
Etsugoya and Tsubakihara in The Impossible Stairwell both have some trouble with tenses before deciding to "just pick one tense and stick to it".
The Time Warp Trio book 2095 has the Trio return from the future and decide they need to leave a Time Capsule for their grandkids to complete a Stable Time Loop "or else they won't be able to save us before now ... or is it after then?"
In the 1632 series, about a 20th century West Virginia coal mining town sent back in time to the middle of the Thirty Years' War, both "uptimers" and locals of the 17th century are often found groping for a way to describe what for the West Virginians would be settled history but hasn't yet happened (or, more likely, will never happen thanks to the Butterfly Effect) for those living during the Thirty Years' War.
Kryten: Actually sir, we don't ever have existed here anymore, but this is hardly the time to be conjugating temporal verbs in the past impossible never tense!
Truth in Television — The tenses were so difficult that Robert Llewellyn, playing Kryten, kept flubbing the line and eventually had to have a cue-card held up out of shot... and then the line was cut anyway. It only resurfaced as they showed the final correct take after all the bloopers in the Smeg Ups collection.
Seventh Doctor:An anti-gravitation matter transmitter. Didn't you give me this next year?
In "The Beast Below," Amy ends up encountering the Time Travel Tense Trouble, telling a little girl she's getting married "a long time ago tomorrow morning." Which does technically make sense in the same way as "a week tomorrow".
In "The Vampires of Venice" Rory says he's getting married in 430 years...which is why they have to have this conversation RIGHT NOW.
In "The Vampires of Venice": The Doctor says the girls are like Houdini "He was shorter. Will be shorter. I'm rambling..."
In the short comic relief specials "Space" and "Time"; Rory and Amy get to meet their past (future?) selves, and get confused when explaining that the Doctor will tell them to go back, to tell themselves this, in order to make a Stable Time Loop.
A non-comedic use: Rose, in 'The Parting of the Ways', is sent back home to avoid a bloodbath taking place in the future. Jackie brushes it off, but it tears Rose up enough she tears up other things..
In the Eleventh Doctor episode "The Doctor's Wife," Idris!TARDIS in addition to liking biting (it's like kissing, only there's a winner!) has some initial trouble clarifying her tenses. It makes sense, since she's the spirit of the Doctor's vehicle trapped within a flesh body. She jumps across space and time without regard to those silly simian concepts of past, present, and future.
One more quote:
Amy: No, but you told the Doctor you'd see him again when the Pandorica opens.
River: Maybe I did. But I haven't yet. But I will have.
Chronotis: "I am, I was, I will be, Professor Chronotis. Oh dear... we Gallifreyans have never managed to come up with a satisfactory form of grammar to cover these situations.
Some fan attempts to translate the strange "Circular Gallifreyan" script seen in Doctor Who have come to the conclusion that the language is not meant to be read linearly, but circularly. Words and sentences share tangential relationship to each other rather than flowing in straight lines. It would make talking about time travel easier, but also makes it nearly untranslatable.
Even a Time Lord has trouble sometimes:
The Doctor: You need to get me out of the Pandorica.
Rory: But you're not in the Pandorica.
The Doctor: Yes I am. Well I'm not now but I was back then. Well. Back now from your point of view. Which is back then from my point of view. Time travel, you can't keep it straight in your head.
In Goodnight Sweetheart time traveler Gary Sparrow (who is married in the present day but is having an affair with a woman in 1940s Britain) upbraids his friend for cheating on his wife. When the obvious hypocrisy is pointed out to him, Gary replies "That's different. All my indiscretions are in the past. Even my future indiscretions are in the past.".
In Top Gear, when James May described a Saab, while wondering if Saab was going to go out of business before the show was broadcast:
"They say, or said, that it's based on a jet fighter, or was, but it isn't wasn't."
The sisters (Prue in particular) in Charmed always run into difficulty when trying to get their heads around the concept of tenses when time travel is involved.
Prue: We barely got away as it was. ... Is. Will be. You know, I've never been good with tenses.
Topical Panel Games like Have I Got News for You also get confused by tenses when describing something that might happen between recording and broadcast (and might have changed by the repeat. And heaven knows what'll be happening by the time it's on Dave...)
Sometimes averted by having a special Friday Morning recording, usually so an election’s results are known...
Iain: Amazing the candour a politian can show!
Lembit Opik: I'm not a politician any more – I can do what I like!
In an episode of Quantum Leap, Sam leaps into the past version of his friend and helper Al; early on, Al has a bit of tense trouble relating to his younger self ("I think I'm... I mean, he thinks I'm my uncle.") Eventually Sam suggests that they refer to Young Al as "Bingo", which was his Air Force callsign.
Sheldon: Wait, whoa whoa. Is "placed" right? Is "placed" the right tense for something that would have happened in the future of a past that was affected by something in the future?
Leonard: Had will have placed?
Sheldon: That's my boy.
From The Other Wiki's article on the MIT Time Traveler Convention: "The spacetime coordinates continue to be publicized prominently and indefinitely, so that future time travelers will be aware and have the opportunity to have attended."
Parsley Boobs has this exchange between the future counterparts of Carl and Steve:
Steve: Close the door! Don't you know he suffers from amblyopia?
Future Carl: Yes I do... for I are he! Only, I'm from the future.
Future Steve: You know, I really do think it's "I AM he".
Future Carl: It's all this time traveling! It really confuses me as to what tense we should be using!
As with the panel games examples in Live—Action Television. The News Quiz lampshades the folly of having a Topical Panel Show being recorded on a Thursday for broadcast on a Friday as one the most anticipatable news events frequently occurs on a Thursday, an election in the UK. Leading to having to predict (Read:bluff) the result to perform gags accordingly.
Continuum invents a time-travellers' jargon with terms regarding your personal 'spanner' timeline being separate from terms used in the general 'leveller' timeline. Things in your subjective past are in your "age", while things in your subjective future are in your "yet". When talking about objective time, things are either "Up" or "Down"; the year 2000, for example, is Up from the year 1990. All events except those in your personal past require the present tense, since in a second, they may be your "now" too.
The Luteces casually lampshade and debate this in front of the player. Their discussion is very confusing.
Robert: I told you they'd come. Rosalind: No, you didn't. Robert: Right. I was going to tell you they'd come. Rosalind: But you didn't. Robert: But I don't. Rosalind: You sure that's right? Robert: I was going to have told you they'd come? Rosalind: No. Robert: The subjunctive? Rosalind: That's not the subjunctive. Robert: I don't think the syntax has been invented yet. Rosalind: It would have had to have had been. Robert: "Have had to have..?" That can't be right.
Also, in the game's intro, Robert notes that the player "doesn't row". He means that the player never rows, in any of the timelines. Rosalind misinterprets this as "The player doesn't know how to row/isn't a rower.
Rosalind: Why? Robert: Because he doesn't row. Rosalind: He doesn't ROW?! Robert: No. He doesn't row. Rosalind: Ah. I see what you mean.
This doesn't make any sense to me. My readings tell me that your Temporal Scaling isn't strong enough yet to support the mission I had planned for you. But you've already done the mission. I know. I was there.
Made even worse because he's also in contact with a nearly infinite number of alternate selves, some of whom passed the local universe's Do Not Pass Go, Do Not Exist time travel brick wall.
Diviner Maros of the Circle of Thorns exists at all points over a 14,000 year period simultaneously. Your conversations with him can be very confusing, even to him.
Garland/Chaos: "Two thousand years from now, you killed me."
Lampshaded, like everything else, in Kingdom of Loathing. At the beginning of time, all messages are prefaced by "you remember" followed by a past participle or past perfect; the Distant Past switches off between first-person present and third-person past (because you're inhabiting the memories of your ancestor) seemingly at random, and the exposition upon arriving in the future for the first time starts out in future tense before saying "You will then start getting your narrative in present tense, because it's the future, we get it, no need to run that joke into the ground."
Prince of Persia: The Sands of Time naturally falls victim to this trope during the final boss fight. Among the banter we find this: "It happened! ... Well, it will happen!" referring to the events of the game being experienced, rewound, and then about to happen (again?) if the Prince doesn't do something about it.
The Achron fandom made a little of their own grammar to explain stuff in the game. They talk about game-time and real-time (also referred to as "time" and "metatime"), and refer to units and events as early or late. When they specify when something happened, they use an ordered pair for the time.
A boss in Avernum 5 summons two future versions of himself to assist him, and he does his best to keep his grammar consistent when shouting orders to them. He loses track and starts rambling when you kill both future selves and screw up the timeline.
Discworld lets players go back and forth between the past and the present. If you try to use an item that needs to be used at that place but in a different time, Rincewind will say "Try again later. Or earlier."
In The Longest Journey, one of the species April encounters in Arcadia perceives the timeline all at once, and so has a horrible time keeping tenses straight when speaking to more temporally limited creatures.
Amazing Spider-Man: *after the time rift shifts and creates a deadlier path* O’Hara, can you do something to help me in the present? Spider-Man 2099: Which present? You’re in my present. You mean your past present or my present future? Amazing Spider-Man: ...I hate you.
Sarda: You can't do something you haven't yet done differently than how it will come to be done. Fighter: That is the most confusing thing I have ever heard. Black Mage: Two plus two is four. Fighter:Wait.
A truly memorable example occurs referencing Hitchhiker's Guide (the comic in question is indeed titled "Future Semiconditionally Modified Subinverted Plagal Past Subjunctive Intentional"), as Bob, trapped in the future, tries to find out from Prometheus/Protoman how he gets back to the present:
Bob: Okay, if I told you what I did, how did I get back? Prometheus: Don't you mean, if you will tell me what you will do, how will you get back? (Beat Panel.) Bob: How about, if you won't tell me how I did get back, I will shove my boot up your ass?
Described in The Rant for thisTouhou Nekokayou, where it divides temporal conversation between "subjective" (what the time traveller personally experience), "objective" (chronological order), and "metatemporal" (the perspective of changes made to the timeline).
In one Dinosaur Comic, T-Rex likes to assume every unknown historical figure is, in fact, himself on a time travel ("It sounds rad to me!")
Utahraptor: ...I see. So if I said that nobody knows who the historical King Arthur is? T-Rex: I'd say "that's me!" His exploits shall be going to have been being done by me! Utahraptor: Future perfect continuous passive? T-Rex: Ahem. Future perfect continuous passive, BITCHES.
Narbonic: Dave, a long-time chain-smoker, travels back in time and alters the past so that he never started smoking. Later, when he mentions this, his co-workers give him odd looks and comment, "Dave, you never smoked."
Not in-universe, but The Rant for Com'c, is occasionally written the day before the str'ps are posted. Usually when this happens, Krixwell (the author) starts off with a comment where "yesterday", "today" and "tomorrow" are essentially equivalent. From the commentary for str'p #41:
Tomorrow, I'll be continuing what I started two days ago by writing this yesterday, i.e. today. For the record, tomorrow is today, because today is yesterday. Did you see thisnote a link to a different post, which was written after this but posted yesterday?
Meanwhile, I'm off to do whatever I'll be doing yesterday.
Chris Sims of Comics Alliance describes one Plot Thread in the X-Men: "Beyond Good and Evil" storyline thusly:
[Cable and Tyler] are, of course, trying to kill Apocalypse before/after/during his plot to kidnap all the psychics, which may or may not have already succeeded/failed in the future that happened last week. So they need to steal a time machine.
In Kim Possible:A Sitch in Time Shego's future self tries to explain her scheme to take over the world in the future to her present self.
Future Shego: Listen, we don't have a lot of time... OK, actually we do — well... we will.
Present Shego: When you wanna make sense, just let me know.
Future Shego: Grab the Time Monkey!
Present Shego: Why?
Future Shego: You need the Time Monkey.
Present Shego: Can't I just use yours?
Future Shego: No, this is mine! OK, well, actually, it's yours too, I mean... well it's the one you're supposed to steal, so technically...
Present Shego: If you need me, I'm gonna be in there watching Kim Possible lose.
(Later) Kim Possible: But if the Supreme One has the time monkey in the future... or the past... or... Wow. Aah! Brain pain.
Clockwork: I sent him back to his own time... or should I say, forward to his own time? You see, for me, time moves backwards, and forwards, and... oh, why am I bothering? You're fourteen.
My Little Pony: Friendship Is Magic, "It's About Time": Twilight Sparkle receives a message from herself a week in the future, and the state of her future self (wearing a torn black jumpsuit, her mane all messed up, and with an eyepatch and a scar on her cheek) causes her to worry: "What a mess she is. Or I am... or will be!" It turns out her future self was trying to tell her not to panic (which caused her to panic anyway). After she goes back in time to try and deliver her original message, she realizes what just happened and says "Now I'm going to have to worry for a whole week!" despite the fact that for her the ordeal has passed.
Parodied on Family Guy when Stewie and Brian travel through time.
Microsoft Outlook's "Warning: This meeting occurs in the past."
Subversion's error message "Cannot reverse-merge a range from a path's own future history."
Larry Niven called this effect "Excedrin Headache Number SQRT(-π)".
Of course, this problem affects only languages with compulsory tense-marking.
For example, English mandates tense-marking of verbs ("went", "am going" and "will go" for "go", for instance), while Chinese leaves the verb alone and puts time markers around it ("go yesterday", "go now" and "go tomorrow").
This is part of why explaining time modeled as the 4th dimension can be quite difficult.
There is a real life issue with this as anyone who has worked night shift can tell you. Do nights for years and other people remarking about tenses becomes an Overly Long Gag.
When a night shifter talks about waking up and eating dinner, it messes with people's head more than you'd think.
Leaving for work? "Have a good day.. er.. night!"
Eating lunch at 2 AM? That's weird - even though that's what almost everyone calls the meal they eat in the middle of their shift.
People who work at hotels, apartment buildings, etc and other open-24-hour places often are never sure to say "good morning" or "good evening" between midnight and 4 AM, because the early risers are all mixed up with the people returning from a late night out, and each may end up with the person replying "It's not morning/night, it's night/morning!"
Two events separated by a space-like spacetime interval (i.e. every observer will note that light from one event cannot reach the position of the other event before the other event occurs) have no consistent ordering. Different observers will disagree about which event occurred first, and one reference frame will observe the events occurring simultaneously.
Analytically, there are 4 different timescales to be concerned about in speaking: the time of the speaker, the time of the receiver, the time of the event, and the time of the comparative event. In standard life, the first two are equal and the latter two can be present, past, or future to the speakers or each other, leading to the seven standard tenses: present, past, past-past (formally the pluperfect "had"), past future "was going to", future, future-past (or future perfect, "will have"), and future-future (omitted in English and most other languages). If time travel is possible, this means both speaker's and listener's timespans have to be referenced. As these are completely independent of the event timescales, we cannot omit the present tense on either, so we must multiply by three twice for a total possibility of 54 tenses. While some may be omitted as redundant, this still presents a formidable linguistic challenge should time travel ever be possible.
Talk to someone on the other side of the Planet, or really anyone who lives in a time zone significantly different from your own. Watch people say "Have a good night" to someone before saying "Off to lunch, bye!" and everything else.