The World Ends Tomorrow

The world ends tomorrow, but the Big Bad needs one extra night of planning to make sure everything goes as smoothly as possible with their Earthshattering Kaboom.

The heroes are battered and demoralized from their journey up until this point, and there is a very good chance that someone in the party will also be suffering from Heroic BSOD.

Despite the fact the future ends tomorrow, the heroes will always take this time to separate and visit loved ones, have philosophical debates, arm up, or achieve the always popular Last-Minute Hookup. The latter activity can easily be replaced depending on the characters.

Often seasoned with The Apocalypse Brings Out the Best In People as they realize Heart Is an Awesome Power.

Characters may also use this time to finish all of those quests in order to get that one weapon.

Depending on the media, The World Ends Tomorrow may last indefinitely until the heroes go to face the Big Bad.

This trope always takes place immediately before the heroes choose to initiate the Final Battle.

Examples of The World Ends Tomorrow include:

Anime

Summer Wars: A space probe hijacked by a rogue AI is going to crash in two hours, but the only people who have any idea how to stop it still take the time for a family meal together before doing anything. Because that's the way their recently departed grandmother would have wanted it.

Fan Works

A fairly standard cliche in Harry Potter fics is for Harry and his love interest of the week to have one last (or only) fling the night before the Final Battle, most often because they want something to remember him by "just in case" or because Harry doesn't want to die without ever having felt loved.

Film

Apollo 13 has a scene just before their launch when the crew get to say goodbye to their families.
In Armageddon the roughnecks all go out to have some downtime between training and launching the shuttles. Some go to a strip club and get arrested. Chick goes to his ex-wife and gets told off for violating the tenets of their divorce. Grace and AJ get engaged.
Mystery Men shows the heroes saying goodbye to loved ones, and finding the resolve to fight Casanova Frankenstein when The Shoveler gives an inspiring speech (threatening to eat an unhealthy egg salad sandwich should they not fight).
Parodied in the South Park movie, using a Suspiciously Similar Song version of "Tonight".
Spies Like Us After the missile is launched and they realize that an all out nuclear war is about to begin, the protagonists and the Soviet troops split up into pairs and go off to have sex. Then Austin Millbarge has an idea of how to stop the missile...
West Side Story - the "Tonight" medley, showing everyone's preparations to the big Jets versus Sharks battle.

Live Action TV

Buffy the Vampire Slayer Season 3 has the night before Graduation Day, the day the Mayor is going to turn into a giant snake. In the mean time, Willow and Oz finally have sex.
On an early episode of Sliders they were on a world that was about to be destroyed by an asteroid. Quinn works on trying to find a way to leave that world using the tech left behind by that world's Quinn, and Wade insists that he stop so they can talk about their feelings. (Meanwhile Arturo is working to actually solve the problem and Rembrandt is partying like it's 1999.)
The night before the final battle on Angel the team went their separate ways for one last night of whatever.

Video Games

Almost every Final Fantasy game.