Without hesitation (9)
(Other definitions for instantly that I've seen before include "Immediately, forthwith" , "With no delay, this very second" , "Without delay or hesitation" .)
'without hesitation' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for readily that I've seen before include "Without demur" , "Willingly, quickly" , "Willingly, without reluctance" , "Without difficulty or delay" , "in a willing manner" .)
'without hesitation' is the definition.
(in a flash means immediately)
This is all the clue.
(Other definitions for in a flash that I've seen before include "pictures may be taken" , "Instantly, straightaway" , "How lightning appears" , "Almost instantly" , "Where American detected electricity" .)
'without hesitation' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for now that I've seen before include "At the present time" , "Today" , "The present moment" , "Immediately" , "straight away" .)