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

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:

Note that in some varieties of English people say "on the weekend" and "on Christmas".

Notice the use of the prepositions of time in and on in these common expressions:

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)