Q: I feel really confused about how to handle times of day. Should I use numbers or words? Am I allowed to use both “o’clock” and "a.m./p.m.” in my manuscript, or do they all have to be the same?
A: Both in life and in writing, time can be a complicated thing, so we’re glad you asked. In general, you want to follow The Chicago Manual of Style's rule 9.37 for time. Briefly, it says:
Times of day in even, half, and quarter hours are usually spelled out in text. With o’clock, the number is always spelled out.
Numerals are used when exact times are emphasized. Chicago recommends lowercase a.m. (ante meridiem) and p.m. (post meridiem), though these sometimes appear in small capitals, with or without periods. (Note that the abbreviations a.m. and p.m. should not be used with morning, afternoon, evening, night, or o’clock.)
And you do want to be consistent, but only within each use case. It doesn’t matter if you use a.m./p.m., o’clock, and in the morning/at night throughout the same work—just make sure that in each of those cases, you're using the same treatment. Part of your editor's job is to search for each of those uses and check your work to make sure that it's internally consistent.
So to review:
- o’clock: This is an easy one: it’s always spelled out (ten o’clock, four o’clock, etc.), whether in narrative or dialogue.
- in the morning/in the afternoon/at night: In narrative, this is spelled out if it’s a whole or quarter hour (four in the morning, three fifteen in the afternoon) but rendered numerically if it’s an exact and nonrounded time (4:26 in the morning, 3:17 in the afternoon).
- a.m./p.m. In narrative, you’ll want to use numbers in this construction. It’s generally acceptable to use either 10 p.m. or 10:00 p.m.—just make sure it’s consistent for all whole times; you don’t want zeros in some and not in others.
Hope this helps!
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