"We in the trade call this 'Excedrin Headache Number √-3.14159..."
— Larry Niven, The Theory and Practice of Time Travel
Carl Honduras: I ARE he! ...Only I'm from the future.
Minky Steve: You know, I think it's I AM he.
Carl Honduras: It's all this time travel; it makes me very confused as to which tense we should be using.
Minky Steve: There, there. It is very tricky.
Stephen Colbert: So, what did you have planned for us? How did that will go? I look backward to having seen it.
Jon Stewart: You're hurting my brain, Stephen.
Stephen Colbert: Come on, Jon! Don't you want people to have already watched your show?
"It begins to dawn on you that everything you are about to do may prove to have been a colossal waste of time."
Harry's voice trailed off into the inadequacy of English.
Dark Helmet: What the hell am I looking at? When does this happen in the movie?!
Colonel Sandurz: Now. You're looking at now, sir. Everything that happens now is happening now.
Dark Helmet: What happened to then?
Colonel Sandurz: We passed then.
Dark Helmet: When?
Colonel Sandurz: Just now! We're at now, now.
Dark Helmet: Go back to then!
Colonel Sandurz: When?
Dark Helmet: Now.
Colonel Sandurz: Now?
Dark Helmet: Now!
Colonel Sandurz: I can't.
Dark Helmet: Why?
Colonel Sandurz: We missed it
Dark Helmet: When?
Colonel Sandurz: Just now.
Dark Helmet: When will then be now?
Colonel Sandurz: Soon!
Dark Helmet: ...how soon?
Funny, you didn't hear any commotion or gunplay. But it looks like there's already been some action in here. Or there will be. You can never take tense for granted with these goons.
The major problem is quite simply one of grammar, and the main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveler's Handbook of 1001 Tense Formations. It will tell you, for instance, how to describe something that was about to happen to you in the past before you avoided it by time-jumping forward two days in order to avoid it. The event will be described differently according to whether you are talking about it from the standpoint of your own natural time, from a time in the further future, or a time in the further past and is further complicated by the possibility of conducting conversations while you are actually traveling from one time to another with the intention of becoming your own mother or father.
Most readers get as far as the Future Semiconditionally Modified Subinverted Plagal Past Subjunctive Intentional before giving up; and in fact in later editions of the book all the pages beyond this point have been left blank to save on printing costs.
The Hitchhicker's Guide to the Galaxy skips lightly over this tangle of academic abstration, pausing only to note that the term "Future Perfect" has been abandoned since it was discovered not to be.
"Can we get some food? I haven't eaten since later this afternoon."
— Aaron, Primer
"The Borg magic up a temporal vortex to travel back to the past, resulting in the present being altered so that the Earth looks like Al Gore's worst nightmare. The only option is to follow them through the space-time wardrobe and stop them from assimilating Earth in the past. Which turns out to be our future, or, at least, our future right now, or... carry the one... Later."
"From there, we cut back to the year 3999, where Cable and Cable Jr...because APPARENTLY THERE WASN’T ENOUGH CONFUSING NONSENSE HAPPENING ALREADY. They 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.
Robert Lutece: If we could perceive time as it truly was—
Rosalind Lutece: —what reason would grammar professors have to get out of bed?
Doc Brown: (the DeLorean has just made the first time-jump) Ah! What did I tell you? 88 miles per hour! The temporal displacement occurred exactly 1:20 a.m. and zero seconds!
Marty McFly: Ah, Jesus Christ! Jesus Christ, Doc, you disintegrated Einstein!
Doc: Calm down, Marty. I didn't disintegrate anything. The molecular structure of both Einstein and the car are completely intact.
Marty: Then where the hell are they?!
Doc: The appropriate question is, "When the hell are they?" You see, Einstein has just become the world's first time traveler! I sent him into the future. One minute into the future to be exact. And at precisely 1:21 a.m. and zero seconds, we shall catch up with him and the time machine.