Do not use “o’clock.” If someone says “6 o’clock,” type “6:00.” Only use “a.m.” or “p.m.” if the words evening/afternoon/night or morning follow (e.g. 6:00 p.m.).
Otherwise, leave just the time (e.g. 6:00).
If the time is mentioned without the word “o’clock”, type out the time numerically. E.g:
I left at nine —> I left at 9:00.
Military time
Military time uses four numbers without a colon. The first two numbers show the hour, and the last two numbers show the minutes. For example, 9:45 a.m. would be written 0945 and spoken zero nine forty-five.
Examples:
My shift went from 1900 until 0700.
It’s 6:00 p.m. (Spoken as “[It’s six o'clock in the afternoon]”)
He’s meeting me at 7:00. (Spoken as “[It’s seven o’clock]”)