time and a half vs rate of pay

time and a half and rate of pay both are nouns.

Word	Noun	Adjective	Verb	Adverb
time and a half	Yes	No	No	No
rate of pay	Yes	No	No	No

As nouns, rate of pay is a hypernym of time and a half; that is, rate of pay is a word with a broader meaning than time and a half:

time and a half: a rate of pay that is 1.5 times the regular rate; for overtime work
rate of pay: amount of money received per unit time

Other hypernyms of time and a half include pay rate.

time and a half (noun)	rate of pay (noun)
a rate of pay that is 1.5 times the regular rate; for overtime work	amount of money received per unit time