Head count at ball around two hours before midnight? (10)
I believe the answer is:
attendance
'head count' is the definition.
(count of how many people attended something)
'at ball around two hours before midnight?' is the wordplay.
'ball' becomes 'dance' (ball can mean an event for dancing).
'around' indicates putting letters inside.
'two hours before midnight?' becomes 'ten' (ten o'clock).
'at'+'dance'='atdance'
'atdance' placed around 'ten' is 'ATTENDANCE'.
(Other definitions for attendance that I've seen before include "People present" , "Turnout" , "Service" , "Gate - enact Dante (anag)" , "Act of being present" .)