showtime vs starting time

showtime and starting time both are nouns.

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

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

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

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

showtime (noun)	starting time (noun)
the time at which something is supposed to begin	the time at which something is supposed to begin