Whenever ready (2,4)
I believe the answer is:
at will
'whenever ready' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for at will that I've seen before include "take it as I please" , "Fire .. .... - whenever you're ready" , "Freely" , "Whenever one pleases, own choice" , "when one wants" .)