You don't pick the time of the show. The system does if you're booking online. If it doesn't give you the show you want you need to try again until it does. If your reservation doesn't say candlelight processional and it doesn't have a show time, the you don't have a CP package reservation.
Anybody looking for Rose & Crown for 6:45 show, I was trying to make that one on the phone yesterday and the CM said the system was allowing selection of that showtime but the booking would not go through. Any other showtime would go through, but not that one. This error appears to be continuing today.
You need to get there more than 15 minutes before the show. Around that time they open up the remaining space in the seating area and let anybody sit there. By that time, groups may have to split up. So, no, seating is not completely guaranteed. If you get there in time, it is, but it doesn't mean you can walk in at the last minute and space for your entire party will be waiting for you. Get the seats, and then let some of your group wander and come back if they don't want to wait.