The first is the soldier on the beach, whose story lasts a week.
The second the men in the boat, who's story lasts a day, the last day of the soldiers week.
The third the pilot in the aircraft, who’s story lasts an hour, the last hour of the last day of the soldiers week.
The film intercuts between all of these, transforming them into one story.
So you would need an event taking place across three interacting but generally separate zones of action.
It's difficult to think of anything more perfect than Land, Sea and Air. D&D has its planes of course, and that gives us the perfect method for introducing different time signatures because what could be more intuitive than the land of the Dead having slower time than, for instance, the Plane of Fire?
Lets say a battle on the border of the Plane of Shadow, involving skeletons and ghosts, with involvement from the Plane of Life, or whatever the equivalent of that is in D&D, something involving plants, Dryads, tree-people etc, then finally in the last hour the Plane of Fire comes into contact as the final decider.
And you would need necessary end of the events of the slower time-planes to be in some sense fixed, so that, by the point that the last (fastest) plane comes into action, its actions are still meaningful and will have some effect.
Then we come into the deep problem with all time-fiddly stuff and roleplaying - maintaining meaningful choice. But if the PCs were part of a larger conflict, relatively minor parts, not deciding heroes, then the general structure of the thing could be decided ahead of time and they could still make meaningful choices _inside_ that structure on their own scale of action. Then when we get to the end it turns out actually they were super-important.
So it would go;
- Death World - Drones in a larger conflict
- Plant World - Still kinda drones but at least they know more. Might do something useful.
- Fire World - Actually super-important thank you very much.
So, off the top of my head; Bad Chaotic Death-Lord is besieging a mega-castle with a planar gateway inside, gonna lead his Skeleton Boyz into IRL. 'Good' Lawful Death-Lord is trying to stop him as the main job of being dead is staying dead.
Its a giant attritional WWI conflict with Skeletons digging trenches and huge war machines on each side. The bad guys are aiming for the PLANAR GATE. "If they reach it they will have access to all possible worlds, and be able to re-write history!" And it looks like the Good Guys are losing, or at least being pushed back.
So the scene sequencing might go...
ONE – INTROS
Death - Intro to the attritional Skeleton war PCs are drafted into. Oh gosh look how terrible it is and how fucked we are. The planar fortress has but a week to stand. Things are certainly happening on a GIGANTIC SCALE, in which we are but _drones_. We are certainly minor characters in _this_ conflict.
Plant - "Hey Plant Queen, is me/us those PC's. Remember your ancient agreement with that likeable Death Guy not to allow reality to get skullfucked by Skeleton ISIS? Well the Castle is a day away from falling and we need you help like now!"
Fire - PCs inform Burninating fire spirits about the Castle falling in like, an hour, and they set off for last-ditch special-forces intercept. Grab the PCs on the way there. Or maybe this is an explanation scene with the PCs begging for aid & trying to persuade them.
TWO - THE BIG PUSH
Death – In the middle of resisting a giant assault the PCs find out that those bad-guys are trying to hatch doom-vultures or something. looks like they will be ready in a week. Perhaps someone with initiative and imagination will decide to do something about that.
Plant - Plant Girls arrive at the start of the last day, another chance for a large-scale overview. Yes this does look utterly fucked. But it looks like someone brave has launched a last-minute counterattack towards that Giant Glowy thing which may be the Key To Victory so lets join in.
Fire - Fire Dudes flying about through space. Things at the Reality Castle look utterly, utterly fucked, some baddies virtually at the gate and the counter-attack against the Big Glowy Thing has stalled with troops pinned down. Better help them out. Look out! Its goddamn Doom-Vultures! Luckily/Unluckily the PCs did/didn't do something about that.
THREE - GONDOR CALLS FOR AID
Death – It’s the last day & someone needs to run for help to the Plant World, maybe the PC's? "We're fucked here, go and call on the ancient Dryad Pact". PC's run off and hopefully end up in the Plant Scene from Section One.
Plant - 'I'm losing too many Root Sisters, go and call on my questionable half brother in the Fire Kingdom". "Go quickly, the castle falls in an hour!" PC's turn up in the Fire scene for section one.
Fire - Ah fuck from up here we can see they have a SUPERDEMON SUMMONING CRYSTAL. We can try to take it out but that would be CERTAIN DOOM. We are going to be extremely reserved and Macho about it.
FOUR - TIME CROSS
Death - It's the big push guys, we need to sally forth and try to take that Glowy Thing in the enemy lines. If we do that then we can win and if we don't, well slip below 50% on Rotten Tomatoes... Who will lead us out of the trenches - probably those dudes!
Plant- I think here Fire and Plant cross times? Maybe we see a fire dude fall out of the sky and have to try to rescue him? But will there be anyone left to rescue? And maybe it’s all pointless anyway? Gasp. Fight your way to the crash site!
Fire - The Fire Dude the PCs are being carried by falls out of the sky, probably blasted by that SUPER DEMON, they already know how long it’s going to take to be rescued as they did that in the last scene so they just need to hold in the impact crater, protecting this wounded guy, until the Plant People from the previous scene show up. Were they fast enough?
FIVE - CLIMAX - UNIFIED TIME
Death - We're nearly there! Despite heavy resistance we have almost reached the Big Glowy Thing, but what's this? A secret SUPER DEMON. If only we had some convenient allies. Gotta hold the line and hope help falls out of the sky.
Plant - We've (probably) rescued that downed Fire Guy, look, on that ridgeline, some familiar-seeming characters locked in battle with a SUPER DEMON - looks like they need some help. Lets go!
Fire - "I might have been shot down by those assholes but thanks to you guys saving me I can get you round the flanks of this battle. While the Skeleton Bros fight the SUPER DEMON and the Plant Girls take it in the side, I can get you to the Big Glowing Thing! And with my FIRE POWERS I can melt the shit out of it!"
Oh fuck its MAIN VILLAIN - right here, next to their Superweapon with everyone present in the same time signature!
And then it’s just a standard fight.
I think the only way this is going to work is if the PCs split up, or if they maybe have dual or triple souls due to being actually-alive people and that means different parts of their souls can go to different parts of this fractured reality, like the multi-part souls of Ancient Egyptians, who based their beliefs on Arnold K's Centerra...
There is also the possibility of using D&Ds actually-different realities to have the battle happening across all three planes at the 'same time' but the times themselves are compressed depending on what level of reality they are coming from. Though that would be a challenge to conceive.