Very quickly (2,1,5)
'very quickly' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for in a flash that I've seen before include "pictures may be taken" , "Where American detected electricity" , "Very quickly" , "Almost instantly" , "Instantly, straightaway" .)
'very quickly' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for in no time that I've seen before include "Very rapidly, hardly measurable" , "Very quickly" , "Without delay, too quick to measure" , "Very rapidly - but sounds impossible?" , "Immediately" .)
(Other definitions for fast that I've seen before include "Quick - don't eat" , "Abstain from food/drink" , "Sporting quickie?" , "Quickly; tight" , "Flying" .)