Prepositions of time
At, on, and in
We use at for specific times.
I start work at 7.00 a.m.
I don't work at night.
We use on for specific days and dates.
My birthday is on Monday.
We're having a party on 7th September.
We also use on for some special days.
On Christmas day.
We use in for nonspecific times during a day, a month, a season, or a year.
In summer it's too hot to work.
I started this web site in 1999.
She woke up in the night.