hours vs period of time

hours and period of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
hours	Yes	No	No	No
period of time	Yes	No	No	No

As nouns, period of time is a hypernym of hours; that is, period of time is a word with a broader meaning than hours:

Other hypernyms of hours include period, time period.

hours (noun)	period of time (noun)
a period of time assigned for work	an amount of time
an indefinite period of time