Haven't seen that, but the truly international measure of time would probably be UTC. (And/or GMT, which is virtually identical to that and all the other slight variants[1], for all intents and purposes, and of course you'd ignore the switch to BST in summer.)
[1] Each of which claiming to be more accurate to the Earth's spin, or to celestial movements, or keyed to a given atomic clock.
Why would the North Pole be UTC?
Why would it be anything else? I'm just suggesting that "Zulu hour" is a more logical standard than any other, in the absence of any locality-based cues. Bits of Greenland are UTC+-0 (although that's more because of locale, other bits are up to UTC-4 adrift). Scott-Amundsen base at the south pole uses UCT+12/13 to match New Zealand (IIRC), so some link of
that kind might be used, I suppose. (I think there's an Arctic link to Bergen or Oslo's tz, which is probably +1.) What's the ISS? It could be on Houston time (although it's International, so while Mir was probably on Moscow time, that sounds like a bad bias), but it's probably UTC-based, if at all, regardless of the rapid sunset/sunrise cycles they encounter. (The reverse happens for the Mars Rover controllers. They tend to sych their Earthly base, and even their own sleep cycles, to martian 'sols' (about 40 minutes longer than Terran day's), but there are varying schemes in use to cater for this dislocation. And that doesn't apply at all to our own planetary poles, so forget I mentioned it.)
and why is it so important that it's 5AM UTC?
Like I said, I've not seen the film. How about we nitpick that idea, though... oh, wait...
EDIT: I was going to mention that the International Date Line isn't even at UTC, but I wasn't sure of the relevancy.
Of course it isn't. It shifts back and forth at different latitudes, to satisfy local geopolitics, but
theoretically is at the midpoint of the UTC+-12 transition area.
Anyway, everyone knows how Santa does it (magic!), so anyone else given the job (or a similar one) is undoubtedly similarly endowed with time and/or space-bending abilities. Especially whatever the thing that makes the ratio of chimney/ventilation duct/letterbox/keyhole diameter to Santa-girth a value greater than one...