Preposition use — in / at / on — prepositions of time and date
Use 'in' months and years and periods of time:
in the twenties
Use 'in' a period of time in the future:
in a few weeks
in a couple of days
Use 'at' with precise time:
at six o'clock
at two p.m.
Use 'on' with days of the week:
Use 'on' with specific calendar days:
on Christmas day
on October 22nd
in the morning / afternoon / evening — at night
We say in the morning, afternoon or evening BUT we say 'at night'