Clarification of Time Notations
However, because practical confusion is still possible, some style guides recommend replacing "12:00 p.m." with "12:00 noon" and "12:00 a.m." with "12:00 midnight".
Clearing Up AM and PM
Technically, it is correct only to call it 12:00 noon. Likewise, the middle of the night is 12 o’clock midnight.
Understanding Morning and Evening Notations
If you want to set up a meeting that starts at noon, you would set it to start at 12 PM. If you would like to set up a meeting to start at midnight, it would start at 12 AM.The first 12-hour period is designated as am. It runs from midnight to noon. The second period, marked pm, covers the 12 hours from noon to midnight.
AM and PM Explanation
AM and PM are the abbreviated terms for Ante meridiem and Post meridiem which means before noon or midday and afternoon or midday respectively. The initial 12-hour period which lasts from midnight to noon is designated with AM while the next 12-hour period which lasts from noon to midnight is designated with PM.
In the U.S., afternoon hours typically mean noon (12 PM) until 3 PM. Late evening starts around 7 PM, and 9 PM is generally when "Night" begins.