over and over again vs time and time again

over and over again and time and time again both are adverbs.

Word	Noun	Adjective	Verb	Adverb
over and over again	No	No	No	Yes
time and time again	No	No	No	Yes

As adverbs, over and over again and time and time again are synonyms defined as:

Other synonyms of over and over again include again and again, over and over, repeatedly, time and again.

over and over again (adverb)	time and time again (adverb)
repeatedly	repeatedly