uptime vs period of time

uptime and period of time both are nouns.

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

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

uptime: a period of time when something (as a machine or factory) is functioning and available for use
period of time: an amount of time

Other hypernyms of uptime include period, time period.

uptime (noun)	period of time (noun)
a period of time when something (as a machine or factory) is functioning and available for use	an amount of time