Follow the guidelines in the Chicago Manual.
A few general guidelines include:
Use numbers to refer to time in most instances. In most editorial text, references to a.m. and p.m. should be lowercased and include periods.
- The class begins at 8 a.m. and ends at 9:10 a.m.
Use noon (instead of 12 p.m.) and midnight (instead of 12 a.m.)
When it’s important to note the time zone, include a three-letter abbreviation in parentheses after the reference to the time.
- The webcast takes place at noon (EST), Saturday, October 15.