day-and-night vs nonstop

day-and-night is not a noun while nonstop is a noun.

Word	Noun	Adjective	Verb	Adverb
day-and-night	No	Yes	No	No
nonstop	Yes	Yes	No	Yes

As adjectives, day-and-night and nonstop are synonyms defined as:

Other synonyms of day-and-night include around-the-clock, round-the-clock.

day-and-night (noun)	nonstop (noun)
	a flight made without intermediate stops between source and destination

day-and-night (adjective)	nonstop (adjective)
at all times	at all times
	(of a journey especially a flight) occurring without stops

day-and-night (adverb)	nonstop (adverb)
	without stopping