time of day: numerals, noon, and midnight

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.