straight off vs instantly

straight off and instantly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
straight off	No	No	No	Yes
instantly	No	No	No	Yes

As adverbs, straight off and instantly are synonyms defined as:

straight off and instantly: without delay or hesitation; with no time intervening

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

straight off (adverb)	instantly (adverb)
without delay or hesitation; with no time intervening	without delay or hesitation; with no time intervening
	without any delay