time of year vs period of time

time of year and period of time both are nouns.

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

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

time of year: one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions
period of time: an amount of time

Other hypernyms of time of year include period, time period.

time of year (noun)	period of time (noun)
one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions	an amount of time