Period of time without energy? Heading for detox unit (4)

I believe the answer is:

yard

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'unit' is the definition.
(I have seen 'Unit of length' mean 'yard' so perhaps 'unit' could also mean 'yard')

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for yard that I've seen before include "quantity of ale" , "Enclosed area; length" , "American garden" , "Measure of length" , "Three feet - enclosed area" .)

I've seen this clue in The Independent.

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