Don't sit up - go off duty (5,4)

I believe the answer is:

stand down

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'go off duty' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for stand down that I've seen before include "Relinquish one's post" , "Withdraw from post or competition" , "Exhibition equipment packed up" , "Withdraw voluntarily, from job or competition" , "Withdraw; go off duty" .)

I've seen this clue in The Irish Independent.

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