Conference delegate two hours before midnight intensely scratching backside (8)
I believe the answer is:
attendee
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for attendee that I've seen before include "One at a meeting; teen date (anag.)" , "One present at a meeting" , "Someone who is here" , "Conference participant" , "One going to, eg, conference" .)