One problem I can see is the location of the two venues. The sing-along is at the front of the park, Sci-Fi is in the middle. After sitting for the time for the sing-along some personal needs might have to be taken care of. You would only have ten minutes to exit the sing-along and make it back to Sci-Fi. You do have a grace period for the seating, which has been mentioned, and I don't know the make up of your party or how quickly you can exit the sing-along but if you could push back your seating just ten minute, you will be fine. Otherwise, I'd say go for it and I'm sure you will be accommodated when you can.