autumn vs time of year

autumn and time of year both are nouns.

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

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

autumn: the season when the leaves fall from the trees
time of year: one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions

Other hypernyms of autumn include season.

autumn (noun)	time of year (noun)
the season when the leaves fall from the trees	one of the natural periods into which the year is divided by the equinoxes and solstices or atmospheric conditions