bit vs blink of an eye

bit and blink of an eye both are nouns.

Word	Noun	Adjective	Verb	Adverb
bit	Yes	No	No	No
blink of an eye	Yes	No	No	No

As nouns, blink of an eye is a hyponym of bit; that is, blink of an eye is a word with a more specific, narrower meaning than bit:

bit: an indefinitely short time
blink of an eye: a very short time (as the time it takes the eye to blink or the heart to beat)

Other hyponyms of bit include flash, heartbeat, instant, jiffy, New York minute, split second, trice, twinkling, wink.

bit (noun)	blink of an eye (noun)
the cutting part of a drill; usually pointed and threaded and is replaceable in a brace or bitstock or drill press	a very short time (as the time it takes the eye to blink or the heart to beat)
piece of metal held in horse's mouth by reins and used to control the horse while riding
the part of a key that enters a lock and lifts the tumblers
a short performance that is part of a longer program
a small fragment
an instance of some kind
a small amount of solid food; a mouthful
a small fragment of something broken off from the whole
a unit of measurement of information (from binary + digit); the amount of information in a system having two equiprobable states
a small piece or quantity of something
an indefinitely short time