Prepositions of Time

1. at

a. time of the day:

at six o'clock

at lunch(time)

at midnight

at sunset/sunrise

[Note that in questions we usually say: "What time shall we meet?" – not: *"At what time ..."]

b. other expressions:

at night

at the weekend/weekends

[note: American English: on the weekend/weekends]

at Christmas/Easter

at the moment

at the same time

2. on

a. days:

on Friday(s)

b. day + time of day:

on Monday morning(s)

on Wednesday evening(s)

on Sunday afternoon(s)

c. dates:

on December 13, 1965

on Christmas Day

on New Year's Day

on Valentine's Day

on my birthday

on our wedding day

3. in the

a. periodical time of day:

in the morning(s)

in the afternoon(s)

in the evening(s)

b. centuries/decades:

in the 15^th century

in the Middle Ages

in the Stone Age

in the 1980s

c. reference of time:

in the past

in (the) future

[but: at present]

4. in

a. months:

in April

b. years:

in 1978

c. seasons:

in (the) winter

d. a time in the future:

in five minutes

in a few weeks

in a moment

5. no preposition

a. before next:

Let's meet next week.

b. before last:

I saw him last week.

c. before this:

We got up late this morning.

d. before every:

I play badminton every Saturday.

Source : english tutorial