at, on and in: time
at + clock time
at + weekend, public holiday
in + part of day
in + longer period
on + particular day
Clock times: at
- I usually get up at six o’clock.
- I’ll meet you at 4.15.
- Phone me at lunch time.
At is usually left out before what time in an informal style (see here).
- What time does your train leave?
Parts of the day: in
- I work best in the morning.
- three o’clock in the afternoon
- We usually go out in the evening.
Note the difference between in the night (mostly used to mean ‘during one particular night’) and at night (= during any night). Compare:
- I had to get up in the night.
- I often work at night.
In an informal style, we sometimes use plurals (days, etc) with no preposition.
- Would you rather work days or nights?
We use on if we say which morning/afternoon, etc we are talking about, or if we describe the morning/afternoon, etc.
- See you on Monday morning.
- We met on a cold afternoon in early spring.
Days: on
- I’ll ring you on Tuesday.
- My birthday’s on March 21st.
- They’re having a party on Christmas Day.
In an informal style we sometimes leave out on.
- I’m seeing her Sunday morning.
We use plurals (Sundays, Mondays, etc) to talk about repeated actions.
- We usually go and see Granny on Sundays.
Public holidays and weekends: at
We use at to talk about the whole of the holidays at Christmas, New Year, Easter and Thanksgiving (AmE).
- We’re having the roof repaired at Easter.
But we use on to talk about one day of the holiday.
- Come and see us on Christmas Day.
- What are you doing on Easter Monday?
British people say at the weekend; Americans use on.
- What did you do at the weekend?
Longer periods: in
- It happened in the week after Christmas.
- I was born in March.
- Kent is beautiful in spring.
- Our house was built in the 15th century.
- He died in 1616.
Other uses of in
In can also be used to say how soon something will happen, and to say how long something takes to happen.
- Ask me again in three or four days.
- I can run 200 metres in about 30 seconds.
The expression in …’s time is used to say how soon something will happen, not how long something takes. Compare:
- I’ll see you again in a month’s time.
- It’ll be ready in three weeks’ time.
- He wrote the book in a month. (not
… in a month’s time.)
In American English, in can be used in negative sentences, like for, to talk about periods up to the present.
- I haven’t seen her in years.
Expressions with no preposition
At/on/in are not normally used in expressions of time before next, last, this, that (sometimes), one, any (in an informal style), each, every, some, all.
- See you next week.
- Are you free this morning?
- I’m at home every evening.
- We stayed all day.
- Come any time.
- I didn’t feel very well that week.
- We met one day in late August.
These prepositions are not normally used, either, before yesterday, the day before yesterday, tomorrow or the day after tomorrow.
- What are you doing the day after tomorrow?
And prepositions are usually dropped in questions beginning What/Which + expression of time, and in answers which only contain an expression of time.
- What day is the meeting?
- Which week did you say you’re away?
- ‘What time are you leaving?’ ‘Eight o’clock.’
Note that at is usually pronounced /ət/, not /æt/ (see here).
For the difference between in and during, (see here).