early vs ahead of time

early is an adjective but ahead of time is not an adjective.

Word	Noun	Adjective	Verb	Adverb
early	No	Yes	No	Yes
ahead of time	No	No	No	Yes

As adverbs, early and ahead of time are synonyms defined as:

Other synonyms of early include too soon.

early (adjective)	ahead of time (adjective)
at or near the beginning of a period of time or course of events or before the usual or expected time
of an early stage in the development of a language or literature
being or occurring at an early stage of development
belonging to the distant past
very young
expected in the near future

early (adverb)	ahead of time (adverb)
before the usual time or the time expected	before the usual time or the time expected
during an early stage
in good time