Subjective. It seems like it would be a bit confusing, though, if you had to relearn times whenever you travel somewhere (edit: and dates could flip over in the middle of a work day). But maybe you’d prefer that.
If you get rid of timezones they all say the same time, no?
Before they were invented, it was literally just anarchy. People set it to match people they knew. That’s what I was thinking of, but it could also just be one place where noon is at 12:00 PM.
Can you give any more concrete examples? None come to mind beyond habit, which is not an immutable thing.
Well, there’s not a round number of second in a day, or days in a year, for example, since they’re all naturally occurring and arbitrary. And then the Earth turns at a subtly non-constant rate, and people have settled on a seven day week. If you do have timezones, it doesn’t make sense to be inflexible with them when they run up against geography or trade and cultural ties, so they’ll be curvy, and geopolitics will itself change over decades and someone will want to change which one they’re in. All of this is a headache if you just want to do a calendar calculation.