Go to sleep - it's almost twelve (4)
I believe the answer is:
doze
'go to sleep' is the definition.
(I've seen this before)
'almost twelve' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'twelve' becomes 'dozen' (synonyms).
'dozen' with its final letter taken off is 'DOZE'.
'it's' is the link.
(Other definitions for doze that I've seen before include "Sleep fitfully" , "Catnap" , "Nod off" , "Take nap" , "Sleep lightly" .)