Thirteen confused bankers about to sleep (6,5)
I believe the answer is:
bakers dozen
'thirteen' is the definition.
(synonyms)
'confused bankers about to sleep' is the wordplay.
'confused' is an anagram indicator.
'about' indicates putting letters inside.
'to sleep' becomes 'doze' (doze means to sleep).
'bankers' with letters rearranged gives 'bakersn'.
'bakersn' enclosing 'doze' is 'BAKERS DOZEN'.
(Other definitions for bakers dozen that I've seen before include "Additional fare here" , "It might be a bloomer" , "13" , "Unlucky number of loaves?" , "Thirteen loaves?" .)