due vs on time

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

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

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

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

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