like a shot vs instantly

like a shot and instantly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
like a shot	No	No	No	Yes
instantly	No	No	No	Yes

As adverbs, like a shot and instantly are synonyms defined as:

like a shot and instantly: without delay or hesitation; with no time intervening

Other synonyms of like a shot include at once, directly, forthwith, immediately, now, right away, straight off, straightaway.

like a shot (adverb)	instantly (adverb)
without delay or hesitation; with no time intervening	without delay or hesitation; with no time intervening
	without any delay