That's a good idea. But if you really want to be nice, just ask them if it is OK. Most will say OK, and they will remember how nice it was of you to ask. Always leaves a good impression.
I think starting the jackpot a little earlier than 9 pm would help. During the summer, people still have to work, so they would get home a little earlier. Unless you ar planning on a Friday night. Would you mind giving a general area as to where the arena would be? I live south of Granbury, and that would help me to know how far you are talking.