Hours and minutes
Midnight and noon
The preference is to refer to 12:00 a.m. or 12:00 p.m. as noon or midnight, whichever is appropriate.
We arrived at the scene at 12 p.m.
Preferred: We arrived at the scene at noon.
Full hour
When referring to time that is a full hour, the preference is to omit the colon and following zeros.We started the procedure at 8:00 a.m.
Preferred: We started the procedure at 8 a.m.
o'clock
Never use the term "o'clock" after full time has already been shown in numeric form.The patient was seen at 8 a.m.
not
The patient was seen at 8 o'clock a.m.
The patient was seen at 8:15.
not
The patient was seen at 8:15 o'clock.
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