real time vs period of time

real time and period of time both are nouns.

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

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

real time: (computer science) the time it takes for a process under computer control to occur
period of time: an amount of time

Other hypernyms of real time include period, time period.

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

Other hypernyms of real time include period, time period.

real time (noun)	period of time (noun)
(computer science) the time it takes for a process under computer control to occur	an amount of time
the actual time that it takes a process to occur