Prepositions of Time: in, on, at

Same three words, a completely different sorting rule

Tamil handles years, days, and precise times with the same small set of location-style suffixes, without needing three unrelated words. English reuses in/on/at from the place lesson, but the rule for picking one is entirely new: in for broad time periods (months, years, seasons), on for days and dates, at for exact clock times. Don't try to map this onto the in/on/at place rules — memorize the time version as its own separate system.