Prepositions of time (at, in, on)

The three most common time prepositions are at, in, on.

At

Clock times and some fixed phrases:

• at 7 o'clock, at night, at the weekend (BrE), at Christmas

On

Days and dates that include a day:

• on Monday, on 12 May, on my birthday, on Sunday morning

In

Longer periods:

• in the morning / afternoon / evening (but at night)
• in July, in 2026, in winter

No preposition: today, tomorrow, yesterday, every day, last week, next year.