long run vs period of time

long run and period of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
long run	Yes	No	No	No
period of time	Yes	No	No	No

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

Other hypernyms of long run include period, time period.

long run (noun)	period of time (noun)
a period of time sufficient for factors to work themselves out	an amount of time