twenty-four hour period vs twenty-four hours

twenty-four hour period and twenty-four hours both are nouns.

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

As nouns, twenty-four hour period and twenty-four hours are synonyms defined as:

twenty-four hour period and twenty-four hours: time for Earth to make a complete rotation on its axis

Other synonyms of twenty-four hour period include 24-hour interval, day, mean solar day, solar day.

twenty-four hour period (noun)	twenty-four hours (noun)
time for Earth to make a complete rotation on its axis	time for Earth to make a complete rotation on its axis