Question

 

• 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.

Idioms

1. at a time: He went down the steps two at a time.
2. at last: At last, they found the answer to the question.
3. at times: At times, she enjoys a good historical novel.
4. in case of: In case of rain, the people will stay at home.
5. in the beginning In the beginning, they didn't understand English.
6. in the end: In the end, the two policemen caught the thief.
7. in time for: I came in time for the second half of the movie.
8. on occasion: On occasion, I enjoy a good television program.
9. on time: He almost always gets to work on time.
10. on the spur of the moment: We decided on the spur of the moment.