We use:
* at for a PRECISE TIME
* in for MONTHS, YEARS, CENTURIES and LONG PERIODS
* on for DAYS and DATES

Example :
- At (at noon, at sunset, at 10.00 am, at dinnertime, at bedtime etc.)
- In (in March, in 1996, in the next century, in the Ice Age etc.)
- On (on 4 March, on my birthday, on Monday, on independence day etc.)


Look at these examples:
* I have a meeting at 9am.
* The shop closes at midnight.
* Jane went home at lunchtime.
* In England, it often snows in December.
* Do you think we will go to Jupiter in the future?
* There should be a lot of progress in the next century.
* Do you work on Mondays?
* Her birthday is on 20 November.
* Where will you be on New Year's Day?

Example, in sentences :
- The stars shine at night.
- We finished test at the same time
- She is not home at present. Try later!

When we say last, next, every, this we do not also use at, in, on.
* I went to London last June. (not in last June)
* He's coming back next Tuesday. (not on next Tuesday)
* I go home every Easter. (not at every Easter)
* We'll call you this evening. (not in this evening)