999
xkcd #2867: DateTime
(imgs.xkcd.com)
Alt text:
It's not just time zones and leap seconds. SI seconds on Earth are slower because of relativity, so there are time standards for space stuff (TCB, TGC) that use faster SI seconds than UTC/Unix time. T2 - T1 = [God doesn't know and the Devil isn't telling.]
Tried and tested, now gotta brush up those searching skills and use llm to get your work done quicker