exactly vs on the dot

exactly and on the dot both are adverbs.

Word	Noun	Adjective	Verb	Adverb
exactly	No	No	No	Yes
on the dot	No	No	No	Yes

As adverbs, exactly and on the dot are synonyms defined as:

Other synonyms of exactly include on the button, on the nose, precisely.

exactly (adverb)	on the dot (adverb)
indicating exactness or preciseness	just as it should be
in a precise manner
just as it should be