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