lactation vs period of time

lactation and period of time both are nouns.

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

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

Other hypernyms of lactation include period, time period.

lactation (noun)	period of time (noun)
feeding an infant by giving suck at the breast	an amount of time
the production and secretion of milk by the mammary glands
the period following birth during which milk is secreted