Pam wrote to me to settle a debate between the younger and the older employees in her office. Her brief question was this:
4pm or 4:00pm?
My answer: Neither!
Both of Pam's renderings are incorrect. She needs to insert periods and a space before the abbreviation, like this:
4 p.m. or 4:00 p.m.
In email, many people seem to be dropping both the periods and the space, but don't follow the crowd. The prominent style guides do not support that choice. Here is a sampling of recommendations:
The Associated Press Stylebook:
Microsoft Manual of Style for Technical Publications:
The Chicago Manual of Style and Garner's Modern American Usage:
4 p.m. or 4 PM (with PM in small capitals)
The Gregg Reference Manual:
4 p.m. or 4 P.M. (with PM in small capitals)
Whatever style you choose, be consistent. I always use lowercase letters: 4 p.m.
Pam's coworkers were apparently arguing about whether to include the zeros. Omit zeros when the time is on the hour, but include them in a list of varying times like this one:
7:00 a.m. Registration
7:30 a.m. Breakfast
8:00 a.m. Announcements
8:15 a.m. Speaker
Pam, it's time for you and your coworkers to pitch in and get a style manual. See the recommendations on my website.
Does your style guide recommend a different approach to time? If so, please share it here.