enlistment vs time period

enlistment and time period both are nouns.

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

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

Other hypernyms of enlistment include period, period of time.

enlistment (noun)	time period (noun)
the act of enlisting (as in a military service)	an amount of time
a period of time spent in military service