Service one gets, what to do and when at a ball? (10)
I believe the answer is:
attendance
'service' is the definition.
(I've seen this before)
'at a ball?' is the wordplay.
'a ball?' becomes 'tendance' (I can't explain this - if you can you should give a lot more credence to this answer).
'at'+'tendance'='ATTENDANCE'
'one gets what to do and when' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for attendance that I've seen before include "Turnout" , "Presence; gate" , "Act of being present" , "Number at gathering" , "Gate - enact Dante (anag)" .)