at
at 8 o'clock
at 10:30
at midnight, etc.
at night
at the end of...
on
(on) Sunday(s), Monday(s), etc.
(on) April 25, June 6, etc.
(on) Monday morning, Tuesday afternoon, Friday night, etc.
on the weekend / on weekends (always with on).
in
in April, June, etc.
in 2005, 1990, etc.
in the spring / summer / fall / winter
in the morning / afternoon / evening
We do not use at / on / in before next / last / this / every.
- I'm going to Chicago next Monday. (not on next Monday)
- We go on vacation every summer. Last summer we went to Europe.
in five minutes / in a few days / in six weeks / in two years, etc.
- Hurry! The train leaves in five minutes.
(= it leaves five minutes from now)
- Goodbye! I'll see you in a few days.
<..in Basic Grammar in Use>
