clotting time vs period of time

clotting time and period of time both are nouns.

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

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

clotting time: the time it takes for a sample of blood to clot; used to diagnose some clotting disorders
period of time: an amount of time

Other hypernyms of clotting time include period, time period.

clotting time (noun)	period of time (noun)
the time it takes for a sample of blood to clot; used to diagnose some clotting disorders	an amount of time