Date and time are complex because they are social and historical constructs. Everything about them is arbitrary and exists because of arcane historical reasons.

Date and time are complex because they are social and historical constructs. Everything about them is arbitrary and exists because of arcane historical reasons. No regular system of organizing time maps cleanly onto the movement of heavenly bodies because those movements are not regular (hence: leap seconds). You can describe time in a way that is precise, or in a way that is intuitive, but not both, and woe to anyone trying to convert between the representations. Time zones are the worst because they are political tools, changed for political reasons, often with very little lead time. I think of them as a one way function mapping universal time onto the local political reality.