generation vs period of time

generation and period of time both are nouns.

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

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

Other hypernyms of generation include period, time period.

generation (noun)	period of time (noun)
the act of producing offspring or multiplying by such production	an amount of time
the production of heat or electricity
a coming into being
group of genetically related organisms constituting a single step in the line of descent
all the people living at the same time or of approximately the same age
the normal time between successive generations
a stage of technological development or innovation