We just did this exact thing in September. Our ADR was 8am, but they were taking pretty much everyone in the 8-8:20ish window at the same time for seating. We met every princess, ate all the food and our kids did the princess parade and we were out the door in plenty of time. The RD crowd was stampeding towards the line, but we jumped in as we saw them coming. We were off the ride by 9:13am. We did ask for our check as soon as we sat down, so it was settled and we could leave as soon as the kids did the princess parade. It worked out just fine!