Is it am or a.m.? When do I spell out hours? How do I use o’clock?
Three good questions. Here are the answers:
- Use a.m. and be consistent.
- Even, half, and quarter hours are usually spelled out in text. ( half past five, quarter to six)
- When you use o’clock, always spell out the number. ( Five o’clock, not 5 o’clock)
10.41: Abbreviations for time of day
The following abbreviations are used in text and elsewhere to indicate time of day. Though these sometimes appear in small capitals (with or without periods), Chicago prefers the lowercase form, with periods, as being the most immediately intelligible.
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The abbreviations a.m. and p.m. should not be used with morning, afternoon, evening, night, or o’clock.
- 10:30 a.m. or ten thirty in the morning
- 11:00 p.m. or eleven o’clock at night
9.37: Numerals versus words for time of day
Times of day in even, half, and quarter hours are usually spelled out in text. With o’clock, the number is always spelled out. In the third example, the a before quarter is optional.
- Her day begins at five o’clock in the morning.
- The meeting continued until half past three.
- He left the office at a quarter of four (or a quarter to four).
- We will resume at ten thirty.
- Cinderella almost forgot that she should leave the ball before midnight.
Numerals are used when exact times are emphasized.
(Note that the abbreviations a.m. and p.m. should not be used with morning, afternoon, evening, night, or o’clock.)
- The first train leaves at 5:22 a.m. and the last at 11:00 p.m.
- She caught the 6:20 p.m. flight.
- Please attend a meeting in Grand Rapids, Michigan, on December 5 at 10:30 a.m. (EST).
All answers are based on the Chicago Manual of Style Online (CMOS 17) and the Merriam-Webster Online Dictionary.
Thanks for the clarifications on TIME. I always can learn something from Hallard Press “Question of the Week.”
Thank you, Ben. And thank you for your continuous support of Hallard Press and its publications, as well as your wonderful comments!
…Nancy