starting time vs commencement

starting time and commencement both are nouns.

Word	Noun	Adjective	Verb	Adverb
starting time	Yes	No	No	No
commencement	Yes	No	No	No

As nouns, starting time and commencement are synonyms defined as:

starting time and commencement: the time at which something is supposed to begin

Other synonyms of starting time include beginning, first, get-go, kickoff, offset, outset, showtime, start.

starting time (noun)	commencement (noun)
the time at which something is supposed to begin	the act of starting something
	an academic exercise in which diplomas are conferred
	the time at which something is supposed to begin