- at for a precise time
- in for months, years, centuries, long periods
- on for days and dates
*On is frequently omitted before the expressions Thuesday morning, Thuesday afternoon, etc.
- I saw her on Xmas day.
- He started work on Monday.
*In some varieties of English people say on the weekend and on Christmas.
- She often goes out at night.
- I have a meeting at 10am.
- I don't usually work at the weekend.
- I stay with my family at Christmas.
- We finished the test at the same time.
- at a time: He went down the steps two at a time.
- at last: At last, they found the answer to the question.
- at times: At times, she enjoys a good historical novel.
- in case of: In case of rain, the people will stay at home.
- in the beginning In the beginning, they didn't understand English.
- in the end: In the end, the two policemen caught the thief.
- in time for: I came in time for the second half of the movie.
- on occasion: On occasion, I enjoy a good television program.
- on time: He almost always gets to work on time.
- on the spur of the moment: We decided on the spur of the moment.