Welcome to your favourite Sci-Fi show, where the intrepid adventurers are about to explore the Beyond yet again. In this episode, though, the plot isn't exactly saving the day. It's more like saving all the days. We open with a sweeping establishing shot of the Pyramids of Southbank, dinosaurs ridden by Chairman Mao and Marie Antoinette stalking past. Something, perhaps never explained, has caused all moments in time to be perpetually present — and somehow all contain the same space, too. Alternatively, your adventurers' journey through the plot is what triggers a Time Crash that results in some kind of chronological collapse. This version is more likely to keep your historical figures and landmarks separate, but even then time isn't going to move, and you're going to be trapped in the entire Universe condensed into a split second.
Either situation might not focus on the science aspect of science fiction too much, and rather than a trapped-in-time situation or frozen timeline mess, everything that the viewer is expected to recognise has been gathered together to be happening at the same time as each other, but time continues moving. This is probably your safer option, as it's a lot less taxing on the mind whilst still being easily recognisable as a result of breaking or screwing up the timeline.
Of course, this happening can also create problems when your main get-out clause is time travel. It may have got you into this mess, but it probably can't help get you out, as either the accepted timeline that you've been galavanting through is in another reality and/or your time machine can't break out of the "now". You're going to have to find a way to reverse what you did to cause it, usually revolving around people meeting that never should, oddly enough, or a massive frickin' space war. There may also be a timer set as to how long you have to fix time before it completely implodes and, well, not to worry about because then nothing will have ever existed.
It's generally accepted that if this happens then you've really messed up. In fact, it might be used in the story as the default way to show The Biggest Time Travel Screw Up Yet, because just putting Hitler in charge wasn't enough of a consequence for your reckless time-hoppers.
Sub-Trope of Time Crash, your all-purpose shop for different ways to affect history (a.k.a. the catalogue of negative time travel effects), this being one of the potential outcomes of bruising up time a bit. Compare Merged Reality and When Dimensions Collide.
See also: Time Stands Still, when everything effectively freezes in place but for a select few — usually the heroes — time keeps moving. If you're one of the people who appear to have frozen, it may well be that you experience all of time at once: it may be explained as a massive effect version of localized time dilation in which you are experiencing time at a natural pace, but it's comparatively so slowly that you appear frozen, whilst you can see non-frozen peoples' entire lifespans pass in a second. Place Beyond Time, for somewhere that exists outside temporal reality, so it's effectively experiencing none of time at once and may have a viewing platform so you can look at all of time at once.
- Crisis on Infinite Earths: During the chaos made in the Multiverse there are multiple different Earths fighting to not disappear at the hands of Anti-Monitor. In Earth-1, time is also collapsing, prompting different time periods to happen at the same time but also, it seems, different continuities of different times as there are multiple unthinkable alliances. This is how there are heroes from the present fighting alongside the post-apocalyptic Wild Man Kamandi, the Wild West Anti-Hero Jonah Hex and the WWII Sgt. Rock against the Anti-Monitor's Shadow Demons.
- Child of the Storm has this happen at the end of Book 1, during the climax of the Battle of London, owing to the emergence of Chthon: reality's falling apart, including the distinctions between past and present. Unusually, even after the problem is resolved, side-effects linger, including pre-Industrial levels of forest cover and more than a few examples of Ice Age era wildlife.
- In Diamond and Silver's Excellent Adventure, the repeated use of certain magic damages the fabric of time, to the extent that random portals to various time periods open up, spilling dinosaurs, historical figures, space ships, and other absurdities into the present.
- Discworld: Ankh-Morpork seems to exist in a range of time periods ranging from the medieval (in the early books as a parody of Medieval European Fantasy) to the Victorian (Unseen University working along college rules, the semaphores standing in for the telegraph). The fact that they exist simultaneously (for an example cited In-Universe, a groundbreaking theater called the Dysk and a huge opera house existing in the same lifetime) is explained by the History Monks doing their best to fix history every time there's a Time Crash.
- Doctor Who: In "The Wedding of River Song", the Doctor attempts to escape his apparent death at the hands of the Silence. River Song, whom the Silence had programmed to kill the Doctor, refuses, and they end up in an alternative timeline where all of time is running simultaneously and beginning to disintegrate. These include details like dinosaurs, Charles Dickens on a talk show and Winston Churchill as Holy Roman Emperor who mentions Cleopatra and downloads.
- Legends of Tomorrow: (Season 2 finale spoilers) In "Aruba", the Waverider crew have to steal a few things from their recent-past selves, all in 1916, because their actions have put them into a reality they didn't mean to create. They try to not bump into the versions of themselves, even though theoretically even meeting other members of the crew would affect... one of their realities. It's unsuccessful, and they have to explain why they'd break the first rule of time travel. Climax comes and all of the Future!Legends die by Bad Future!Reverse Flashes to help the versions of themselves in the reality they haven't screwed up yet escape and prevent the Bad Future. Of course, they now exist and not-exist at the same time from different realities in the same time and space. You can understand how the Present!Legends end up crashing through the time stream into a 2017 with dinosaurs.
- Star Trek: Voyager: In Star Trek Voyager S 4 E 17 The Killing Game the Hirogen invaded the ship, but instead of killing the crew, they discovered the Holodeck technology. They used it to replay all the violent events in the recorded history of the Starfleet database; the crew had their memories altered so they actually thought they were holodeck characters. The Hirogen hurt them, send them to sickbay, and then return them to the simulations (the security protocols were disabled on purpose). And Kim kept adding holodeck projectors all across the ship, at the Hirogens' request. And then, all hell breaks loose when Seven of Nine and Janeway get their real minds restored, and the holodeck limits are broken: The Killing Game pt. 2 has Nazis and allies from World War II (some of the crew members with their minds still clouded, others mere NPC) fighting all across the futuristic Voyager ship, that they consider a Nazi stronghold.
- Noitu Love 2 Devolution: The time period changes in each level because of this.
- At the end of Mr. Peabody & Sherman, the title characters have to fix a rift in the space-time continuum that is dropping historical figures and artifacts into the present day before it ends up at this.
- The concept of "simultaneous time" (which is an oxymoron) or of "time being an illusion" where as far as a person's consciousness is concerned, there is no real "past" or "future", there is only the eternal "Now", for one's current incarnation as well as "reincarnational" selves.
- According to general relativity, this is what would happen if you somehow reached a black hole's event horizon alive: at that point, due to gravitational time dilation, your time relative to the inertial observer frame would slow down to a full stop, and conversely, from your perspective, the "outside" time would speed up infinitely, so all of it would pass in a infinitesimal moment of your own time. Accidentally, it would also mean that in that moment, you would be instantly fried by the infinitely blue-shifted and thus insanely energetic cosmic radiation, as basically all electromagnetic energy the universe will have ever released hits you all at once.
- There is the often considered theory that all of a person's life as they view it is actually in a zoom of memories they experience as that part of the brain shuts down during death, making all of time that they knew taking up a nanosecond of "real time". (Interestingly it incorporates the phenomena of déjà vu and déjà vécu, which in this theory are suggested as people remembering things out of order.)