You used to look at the sun or stars to make an estimate, then we had sundials. For larger time scales, there are tons of archaelogical sites around the world which tracked the solstice, equinox, etc and there's evidence that a few cultures even tracked the full period of the moon's orbit (18.6y).

~250BCE, there was a comedy by Plautus which had in it a poem lamenting the proliferation of sundials, which may or may not have been a parody of some of the attitudes at the time:

    The gods confound the man who first found out
    How to distinguish hours! Confound him, too,
    Who in this place set up a sundial,
    To cut and hack my days so wretchedly
    Into small portions! When I was a boy,
    My belly was my sundial -- one surer,
    Truer, and more exact than any of them.
    This dial told me when 'twas proper time
    To go to dinner, when I had aught to eat;
    But nowadays, why even when I have,
    I can't fall to unless the sun gives leave.
    The town's so full of these confounded dials
    The greatest part of the inhabitants,
    Shrunk up with hunger, crawl along the street.

Swatch Internet Time was almost kind of a thing in the late 90s.

There's for instance: https://en.wikipedia.org/wiki/Traditional_Chinese_timekeepin...

Yes, people make up silly things for silly reasons all the time.

All core systems should run on 64bit UTC posix Epoch date-time stamps, and abstract that into whatever ISO 8601 format local communities think is effective policy. If finer granularity is required to recreate events in non-real-time analysis, than additional sampling interval data with event ordering indexes become relevant.

The Metrology around how a Second was (re)defined is actually really interesting. Considering it started as an arbitrary interval originally derived from some dudes heartbeat. =3

https://www.nist.gov/atomic-clocks/how-atomic-clocks-work/cl...