At bedtime, go to it! (5)

I believe the answer is:

sleep

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'at bedtime' is the definition.
'sleep' can be an answer for 'bedtime' (thesaurus). I am unsure of the 'at' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for sleep that I've seen before include "Wayne _; former Royal Ballet principal dancer" , "Be dormant" , "Slumber" , "''... that knits up the ravell'd sleeve of care'' (Macbeth)" , "Snooze" .)

I've seen this clue in the Evening Standard.

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