We had dinner at Sci Fi about two weeks ago and our ADR was 6:20 with Star Wars starting at 8pm. They were behind a bit when we checked in at a little after 6pm and we ended up getting sat around 6:40pm. Time stamp on pics shows us being done around 7:30pm and we had no problem finding a good spot right in the middle front for the show. That's with a full meal as opposed shakes and the restaurant running a bit behind with ADR's. I think 8pm would be pushing it a bit, especially if they are running behind on getting people sat. I also think 9:15 would not allow you to get there in time since the show would not be over until that time and you would have to swim like a salmon to go against the current of people trying to exit as you are trying to get to Sci Fi. I would try for a time between 7 but before 8 IMO.