I would have thought that you'd be fine. If it is an early seating, my guess is that they seat you whenever you got there...so , if you want more time, perhaps you could arrive for your PS earlier than the assigned time.
However, you should be aware that, for the Pirate Cruise, they are actually asking people to show up at least 15 minutes beforehand to check-in, pay, sign waivers, give you a pager, etc., etc. So, 9:15 is really the time that you are up against for showing up at the GF marina. Also, if you are worried about being tight for time and if you've never been to the GF, you should get whatever info you can in advance on how you get to the GF marina from the monorail stop on the second floor of the GF. It's kind of on the other side of the main building.