Work up to time without good health (4)

I believe the answer is:

till

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'work' is the definition.
(tilling is a kind of working)

I can't explain the rest of the clue.

(Other definitions for till that I've seen before include "not starting yet" , "Shop receptacle for cash" , "Money receptacle" , "Cash found here" , "Shopkeeper's moneybox" .)

I've seen this clue in The Times.

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