Time to arrest the flow of drink, say (4)
I believe the answer is:
when
'time' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for when that I've seen before include "Over what period?" , "As soon as" , "Say it when you''ve had enough" , "At what time?" , "stop pouring the drink" .)