Whisky drinkers may say it is just a question of time (4)
I believe the answer is:
when
'question of time' is the definition.
(I've seen this in another clue)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for when that I've seen before include "As soon as" , "Say it when you''ve had enough" , "Over what period?" , "At what time?" , "stop pouring the drink" .)