Crossword Genius

Time to arrest the flow of drink, say (4)

Ross

I believe the answer is:

when

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'time' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

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(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" .)

I've seen this clue in the Evening Standard.
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