when humans first used clear time divisions of day

wolram

can anyone tell me when humans first used clear time divisions of day, night,
I do not mean terms like sun up or sun down, i mean artifical divisions.

selfAdjoint

Well there are bones from the Cro-Magnon era ( circa -25,000) carved with notches that have been interpreted as counting days between full (or maybe new) moons. So "days" but not "days and nights".

At the other end we have the Babylonians around -2500 who counted daytime hours but not nightime ones, implying they made the distinction.

Somewhere in between people decided to count days and nights separately.

wolram

Yes, i did read about the cro-magon bones some time ago, that idea seems a little tongue in cheek though.