PREPOSITIONS OF TIME
We use at
for times of the day
at 7 o’clock, at breakfast time
in expressions like
at the weekend, at night, at New Year
We use on
days
on Tuesday
dates
on May 17th
We use in for
Years
in 2017
seasons
In summer
months
in August
parts of the day
in the morning
There are other expressions that we can use to talk about frequency. These expressions are used at the beginning or end of sentences, not in the middle.
On Fridays, I go to college by bike.
. every day, every week, every month, ever year . ..
. once a day, twice a week, three times a month
. on Fridays, at weekends
. most days, mostnights, most weeks ...