Humans had a lunar calendar of 13 months, 28 days, that would have been known soon after modern humans showed up, maybe 80-100K years ago. You need to know if you have 1 month, or 10 before the next snow comes.

That would have nothing to do with orbital mechanics or anything, even if you think apollo is riding thru the sky on his chariot, he's doing it in a predictable pattern, and recognizing patterns is basically a super power for humans, it wouldnt take long for them to keep track of it.