Prepositions of Time

Prepositions can also be used to show when something happened.

The prepositions at, on, and in

We use at for specific times.

For example:-
I start work at 7.00 a.m. 
I don't work at night.

We use on for specific days and dates .    

For example:
My birthday is on Monday.   
We're having a party on 7th September.   

We also use on for some special days.   

For example:
On Christmas day.

We use in for nonspecific times during a day, a month, a season, or a year.   

For example:
In summer it's too hot to work.   
I started this web site in 1999.
She woke up in the night.

More prepositions of time