It's almost twelve — have a sleep (4)
I believe the answer is:
doze
'a sleep' is the definition.
(thesaurus)
'it's almost twelve' is the wordplay.
'it's almost' means to remove the last letter (most of the word but not all of it).
'twelve' becomes 'dozen' ('dozen' can be a synonym of 'twelve').
'dozen' with its final letter taken off is 'DOZE'.
'have' is the link.
(Other definitions for doze that I've seen before include "Nod off" , "Take forty winks" , "Snooze" , "Catnap" , "Take nap" .)