time interval vs quantity

time interval and quantity both are nouns.

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

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

time interval: a definite length of time marked off by two instants
quantity: how much there is or how many there are of something that you can quantify

Other hypernyms of time interval include amount, measure.

time interval (noun)	quantity (noun)
a definite length of time marked off by two instants	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