Use 'in' months and years and periods of time:
in January
in 1978
in the twenties
Use 'in' a period of time in the future:
in a few weeks
in a couple of days
AT
Use 'at' with precise time:
at six o'clock
at 10.30
at two p.m.
ON
Use 'on' with days of the week:
on Monday
on Fridays
Use 'on' with specific calendar days:
on Christmas day
on October 22nd
IMPORTANT NOTES
in the morning / afternoon / evening - at night
We say in the morning, afternoon or evening BUT we say 'at night'
