on time vs due

on time is not a noun while due is a noun.

Word	Noun	Adjective	Verb	Adverb
on time	No	Yes	No	Yes
due	Yes	Yes	No	Yes

on time (noun)	due (noun)
	that which is deserved or owed
	a payment that is due (e.g., as the price of membership)

on time (adjective)	due (adjective)
acting or arriving or performed exactly at the time appointed	owed and payable immediately or on demand
payable in installments within a designated period of time	suitable to or expected in the circumstances
	capable of being assigned or credited to
	scheduled to arrive

on time (adverb)	due (adverb)
at the expected or proper time	directly or exactly; straight