afternoon vs daytime

afternoon and daytime both are nouns.

Word	Noun	Adjective	Verb	Adverb
afternoon	Yes	No	No	No
daytime	Yes	No	No	No

As nouns, daytime is a hypernym of afternoon; that is, daytime is a word with a broader meaning than afternoon:

Other hypernyms of afternoon include day, daylight.

afternoon (noun)	daytime (noun)
a conventional expression of greeting or farewell, used to wish someone a good afternoon	the time after sunrise and before sunset while it is light outside
the part of the day between noon and evening