Expressing clock time numbers
Measures of time are expressed as numerals.
Conventional form (11:30 p.m., 12 noon, etc.) is preferable to European or military time and dates (2330 on 25 November 1992). However, use of military time may be used for specific purposes by the dictator and therefore should not be converted.
Use a.m. and p.m. if possible. If unsure which is correct and the exact time is not dictated, don't guess.
If the time given is the full hour, do not add the minutes designation (:00) - use only a.m. or p.m., as appropriate. Do not add o'clock.
The patient has a followup appointment for 9 a.m. tomorrow.
NOT: The patient has a followup appointment for 9 o'clock a.m. tomorrow
He will be discharged after 6 p.m.
NOT: He will be discharged after 6 o'clock p.m.
We started the surgery at 7:45 a.m. and completed at 10:15 a.m.
Time of death was 2:27 a.m.
Noon refers to a specific hour in the middle of the day. Do not capitalize it. Do not use the number 12 with it.
The doctor is expecting to leave at noon.
Midnight is treated the same as noon - it refers to a specific hour in the middle of the night. Do not capitalize it. Do not use the number 12 with it.
He was born at midnight.
She was taken to surgery shortly before midnight.
NOTE: This discussion is only regarding clock time style. For use of clockface reference in anatomic position, see anatomic clockface reference.
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