Turnout two hours before midnight disco? (10)
I believe the answer is:
attendance
'turnout' is the definition.
(I've seen this before)
'two hours before midnight disco?' is the wordplay.
'two hours before midnight' becomes 'atten' (I can't justify this - if you can you should give a lot more credence to this answer).
'disco?' becomes 'dance' (I've seen this in other clues).
'atten'+'dance'='ATTENDANCE'
Can you help me to learn more?
(Other definitions for attendance that I've seen before include "all that turned up" , "Number present" , "Act of being present" , "People present" , "Presence; gate" .)