nighttime vs time period

nighttime and time period both are nouns.

Word	Noun	Adjective	Verb	Adverb
nighttime	Yes	No	No	No
time period	Yes	No	No	No

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

nighttime: the time after sunset and before sunrise while it is dark outside
time period: an amount of time

Other hypernyms of nighttime include period, period of time.

nighttime (noun)	time period (noun)
the time after sunset and before sunrise while it is dark outside	an amount of time