Not working to time when trade is slack (3-6)

I believe the answer is:

off-season

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'trade is slack' is the definition.
I can't tell whether this defines the answer.

'not working to time' is the wordplay.
'not working' becomes 'off' (switched off).
'to time' becomes 'season' (a season is a period of time).
'off'+'season'='OFF-SEASON'

'when' is the link.

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I've seen this clue in The Globe and Mail.

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