I would have the first shuttle at 9:30. If there are older relatives and friends, they may not care to stay for the dancing and might even make plans with each other for a quiet time in the hotel lounge or lobby. Are you sure it will be 9 p.m. before dinner is over? That is 4 hours after the ceremony. Unless the ceremony is very long or you have more than 150 guests for a sit-down dinner, that is quite a time span.