The most common prepositions of time are at, on and in.
Use the preposition in in time expressions, when talking about (i.a.):
- months: The school year starts in August.
- seasons: It is nice to travel abroad in summer.
- general parts of the day: in the afternoon, in the morning, in the evening
Use the preposition on in time expressions, when talking about (i.a.):
- weekdays: What are you doing on Monday?
- dates: I was born on the 22nd of November.
Use the preposition at in time expressions, when talking about (i.a.):
- time or a specific parts of the day: at six o’clock, at noon, at midnight
- holidays: We could go to the beach at Christmas.
- beginning or end of the specific period of time (+ of): at the beginning of July, at the end of the 19th century
Note that prepositions are not used with the following expressions of time: every, last, next, one, this or that:
You’ll be sorry one day.
Other prepositions of time:
- during the lecture
- until the end of March
- since the 1950s
- over the past years
- for a week
- by now