Question: is 11 am early afternoon?
Answer: One refers to the clock and one refers to the sky. The set of words that refers to the clock is: midnight (exactly 12:00 am), morning (from 12:01 am to 11:59 am), noon (exactly 12:00 pm), afternoon (from 12:01 pm to 6:00 pm), evening (from 6:00 pm to 11:59 pm).