time and time again vs over and over again

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

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

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

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

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