twenty-four hour period vs nighttime

twenty-four hour period and nighttime both are nouns.

Word	Noun	Adjective	Verb	Adverb
twenty-four hour period	Yes	No	No	No
nighttime	Yes	No	No	No

twenty-four hour period (noun)	nighttime (noun)
time for Earth to make a complete rotation on its axis	the time after sunset and before sunrise while it is dark outside