time unit vs quantity

time unit and quantity both are nouns.

Word	Noun	Adjective	Verb	Adverb
time unit	Yes	No	No	No
quantity	Yes	No	No	No

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

time unit: a unit for measuring time periods
quantity: how much there is or how many there are of something that you can quantify

Other hypernyms of time unit include amount, measure.

time unit (noun)	quantity (noun)
a unit for measuring time periods	how much there is or how many there are of something that you can quantify
	an adequate or large amount
	the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable