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.]
Ah I've gotten to the point where I have to define what "frame" and epoch each time base is in before I'll touch the representation of time( Unix,Gregorian, etc) .To be honest I'm probably just scratching the surface of time problem.
Hell probably the reason we haven't seen time travellers is we suck at tracking time and you probably need to accurately know your time and place to a very good precision to travel to a given point and we can't say where and when that is with enough accuracy to facilitate where to land. And people don't want to land in the earth's surface or 10000 km away from a stable orbit. Maybe some writer can build that out for a time travel book or to discount it for some reason lol
Then there's continental drift, which as Indiana Jones reminded us this past summer, Archimedes didn't know about when he built his time machine.
Pet peeve: brushing aside the time travel fantasy element, there is not a single shred of evidence of any type of connection between Archimedes and the Antikythera Mechanism.
As if the only person clever enough in Ancient Greece was that one famous dude from Syracuse.
Ionians: "Are we a joke to you?"