time of day: numerals, noon, and midnight
How to write a clock time.
Write clock time in numerals, with a.m. or p.m. lowercase and with periods: 4:30 p.m. Write noon or midnight, not 12:00 a.m. or 12:00 p.m. Ante meridiem, shortened to a.m., means before midday. Post meridiem, shortened to p.m., means after midday. Noon is midday, so it is neither before midday nor after it. Midnight is the other seam. Do not write 4:30 PM.
Examples
Use File it by 4:30 p.m.
Use File it by noon.
Avoid File it by 12:00 p.m.