Time Travel is here and it's time to go to the Cretaceous at last and observe some dinosaurs! But we gotta Race Against the Clock, because by the end of the day that asteroid is going to hit!
But wait, wasn't the Cretaceous period 79 million years long? Wouldn't it be better to go visit it any other day but the one guaranteed to kill you? And must it always be right at the impact zone at that?
This is when The Theme Park Version of prehistory reveals its dark side for time travelers. No matter how sophisticated the method of time travel used, the arrivers will always have to complete their tasks before the asteroid arrives. There is no way around it, sometimes even if you're observing Jurassic or Triassic dinosaurs. And if the Time Travel in question was random, it's even more astounding that EVERY protagonist gets sent back to the exact same date.
This need not apply only to the K-T extinction. Fiction loves to flanderize history into simple compact events and travelers headed to other periods may find themselves in the midst of other disasters, like arriving in Manassas only to find a civil war is breaking out, or visiting Pompeii only for a volcano to erupt. Such a visitor is not looking to change history or see said famous event, they just want to take a stroll and breathe in the surroundings only to realize: "HOLY COW! This 20th century ship I'm on is called Titanic!"
Sometimes this is explained by showing that the protagonists causedthe event in question. It turns out that They Already Changed The Past, and the only reason history books record that particular event happening on that particular day is because the time traveller just happened to appear at that time and place, by chance. Therefore, if the arrival to the date of the disaster was purely an accident, causing it doesn't actually make it more justified.
Related to In the Past, Everyone Will Be Famous. As noted above, it may be part of a Phlebotinum Killed the Dinosaurs plot.
Examples involving the K-T extinction:
In GaoGaiGar, ChoRyuJin's trip to the past coincided with the K-T event because they inadvertently caused it when they pushed the asteroid back through a wormhole to keep it from falling in the present.
In Swing 123's Triassic Park: Into the Past, Calvin and Hobbes end up in the late Cretaceous Period, three days before the K-T Extinction Event.
Subverted in Disney's Dinosaur. Since it's a dinosaur movie, we get the obligatory asteroid strike to kick off the plot, but it's not the asteroid strike—its damage appears to be confined to a relatively small area, and the dinosaurs in the cast manage to survive by migrating en masse to the nearest fertile area.
In Megamorphs 2, a hole in space-time causes the Animorphs to accidentally arrive one day before the asteroid hit. They get into a tussle with several warring Ancient Astronauts trying to colonize Earth, the losing species attempting revenge by diverting the path of a passing comet. The meteor's strike creates another hole that lets the kids return to the present. It was one of the weirder books.
Justified in Pathfinder. The protagonist Rigg can travel back in time by identifying the "path" of a living thing that had walked the land before. In a moment of urgency he picks the most recent path of an extinct animal he sees, which turns out to be fleeing the Colony Drop that rendered it extinct.
The Magic School Bus book In the Time of the Dinosaurs has them escape from the asteroid at the end of their day in the Cretaceous, though also after visiting other periods. It's averted in the corresponding animated episode however, where there is no asteroid because Ms. Frizzle sends them back 67 million years in the past.
Inverted and lampshaded in the Italian children's book Aiuto, c'č un triceratopo in cantina!note Help, there's a Triceratops in the basement!. The time-travelling protagonists want to witness the end of the dinosaurs, but it takes them a lot of trial and error to zero in on the right instant. When another character asks them why they don't quit mucking around and skip directly to the extinction bit, everybody else roll their eyes.
Scientists in Robert J Sawyer's End Of An Era travel back in time to the Cretaceous in order to (of course) study dinosaurs. Because of some uncertainty in the equations, they happen to arrive a couple days before the K-T Event. And for good reason, too. They caused it.
Timeriders likes to play with this trope. The second book involves ending up in the late Cretaceous with a dozen or so civilians, but despite the approximate date (about 62.5 million years BC - geology is wonderfully vague like that) the asteroid is not their primary mortality concern, but (in order) food and water, disease, predators and inbreeding. And the pack of highly intelligent and adaptable predators that have been stalking them for the last month, of course.
Justified in the Star Trek TOS novel First Frontier, where the Guardian of Forever sends the Enterprise crew back to the asteroid strike because someone else has already prevented it.
In the first episode of Prehistoric Park, Nigel must collect a T. rex for the park before the asteroid hits. He justifies this by saying that he wants to get a specimen that would have died anyway so the timestream won't alter too much. However, he later revisits the period on other trips involving significantly fewer asteroids.
Chrono Trigger has you traveling to 65 million BC, and in the conclusion of that part of the plot, a giant asteroid falls to the planet. Justified in that the asteroid that wiped out the remainder of the Reptites is actually Lavos.
Chucko: You think I'm scared? *ignites dual-bladed lightsaber* I'll be running this dump in a few yea... *turns and sees asteroid* Oh phooey...
Chronos, back in the present, then asks the rest of his goons, "Do you know what killed the dinosaurs? Chucko does."
Back to the Future also pulled this out, with Doc Brown and Verne stopping a meteor from hitting to save a dinosaur they befriended, only to find out it was that one, and without it, dinosaurs still rule the earth.
Happens during an Imagine Spot episode in one of Albert Barillé's Once upon a time... cartoon series. The kids are time travelling (with their imagination!) and they stop for a walk 65 million years BC. The storyteller is a bit dumbfounded at first trying to remember why that date is stuck in his mind before he realizes it, gets the children on the time machine and they depart seconds before the asteroid hits. Your Mind Makes It Real... perhaps a bit too much.
The 2003 Teenage Mutant Ninja Turtles zigags this trope. At a point in the Cretaceous Period, the turtles travel back to prevent a plan by a villain that would cause the asteroid in the K-T extinction to narrowly miss the Earth, temporarily lose MacGuffin that would allow them to return to the present for a few days before finding it at the end of the episode. During the episode, we see a bright red dot in the sky that Donatello assumes is the asteroid in the distance, but he admits that he doesn't know when its going to hit and when he doesn't know if they'll get back to the present, he guesses it could be anywhere from weeks to years.
The Disney ride based on Dinosaur mildly averts this by claiming initially you would have gone on a tour of the peaceful early Cretaceous, but a rogue researcher changed your arrival date to just before the extinction event because he wants to rescue Aladar, the film's hero.
Examples involving other historical events:
Time Bandits has Kevin and the dwarves arrive on the Titanic not long before it sinks.
In Doomsday Book, time traveler Kivrin arrives at the start of the Black Death epidemic of 1348, twenty years later than she intended to arrive. The explanation is that history resists people from going to any time but specific dates, hence why she must arrive in 1348.
In Timeline, a medieval history teacher and his students, working in an archaeological dig at a (fictional) ruined castle in France, travel to 1347 - mere days before the castle was taken by the English during the Hundred Years War. The trope is played even more straight when they return to the present and kick the JerkassCorrupt Corporate Executive that built the time machine into the time machine, sending him to the same place... in 1348, just as the Black Plague arrives. Since he never comes back, they assume he caught it and died. The Film of the Book condenses this and just has the guy thrown into the Final Battle in 1347, right in time to get a sword strike to the head.
Timeriders is interesting, as mentioned above. Because of alternate timelines, examples include accidentally landing on the lawn of the White House minutes before a Nazi invasion, prolonging the siege of Nottingham for about a week (in-universe predictions held it to hours at best under the pressure of Richard I's armies) and the fact that one of the team was a steward on the Titanic is explained thoroughly; the Agency needed to know exactly when and where these teenagers would have died. What better than someone known to have been missing in action at the bottom of the ship in one of the most infamous voyages of the twentieth century?
This is often the driving plot device of Doctor Who. The Doctor and his companions will arrive at some key moment in time just before a volcano explodes, a ship sinks or a war breaks out (and usually find an alien plot behind it).
The Doctor: You didn't always take me where I wanted to go.
Idris: No, but I always took you where you needed to go.
Even his trips into the future fit the trope. If he visits anything ever it's practically guaranteed to precipitate large-scale deaths in some incredible fashion.
The Time Tunnel. If the protagonists ended up in a place where a historic event took place, they always arrived just before said event occurred. Indeed, the very first episode sends them to the Titanic.
In The Twilight Zone episode "There's No Time Like the Past" this was being done intentionally at first, as a man goes back in time to attempt to warn the people of Hiroshima about a nuclear bomb in 1945 (hours before it hit), prevent the sinking of the RMS Lusitania (hours before it was torpedoed), and kill Adolf Hitler before World War II. But when he decides to stop trying to change the past and go live in 1881, this trope still comes into play. He arrives the day before President James Garfield is assassinated, but decides to let it happen. Then it turns out he arrived a few days before a huge fire killed some children at the local schoolhouse, and he struggles with whether or not to prevent it, only to end up causing it when he does try to intervene.
Intentionally subverted in Quantum Leap, where Sam's time-traveling missions (as determined by an unknown entity) only involved fixing the lives of normal people, never celebrities. The closest that he came to do so was when he tried to prevent John F. Kennedy's assassination, and succeeded only in saving his wife (who, in the original timeline, had also been killed.)
In the Family Guy episode "Road to Germany", Brian and Stewie travel back in time to Warsaw, Poland (though how they got to Poland from Rhode Island is never explained), September 1st, 1939. The date that Germany invades Poland and kicks off World War II. They have time for one Jewish wedding before tanks start rolling in.