read · 3 min
Think of a ladder from big to small: in for large, on for surfaces/days, at for points.
Time
in 2025, in May, in the morning · on Monday, on my birthday · at 6pm, at night, at the weekend
Place
in a country/room · on a street/floor/surface · at a point/address/event
quick rule
Big container → in. Line or surface → on. Exact point → at.