English pronouns at, in, on

Prepositions of Time: at, in, on
We use:
  

at for a PRECISE TIME in for MONTHS, YEARS, CENTURIES and LONG PERIODS on for DAYS and DATES in MONTHS, YEARS, CENTURIES and LONG PERIODS in May in summer in the summer in 1990 in the 1990s in the next century in the Ice Age in the past/future on DAYS and DATES on Sunday on Tuesdays on 6 March on 25 Dec. 2010 on Christmas Day on Independence Day on my birthday on New Year's Eve

at PRECISE TIME at 3 o'clock at 10.30am at noon at dinnertime at bedtime at sunrise at sunset at the moment

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?

Notice the use of the preposition of time at in the following standard expressions: Expression at night at the weekend at Christmas/Easter at the same time at present Example The stars shine at night. I don't usually work at the weekend. I stay with my family at Christmas. We finished the test at the same time. He's not home at present. Try later.

Notice the use of the prepositions of time in and on in these common expressions: in in the morning in the mornings in the afternoon(s) in the evening(s) on on Tuesday morning on Saturday mornings on Sunday afternoons on Monday evening

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)

See also Prepositions of Place: at, in, on