We got a PS last time hoping to be seated when the fireworks started. We got a table with a castle view, but it wasn't right up against the MK-side window. As a result, we couldn't see the tops of a lot of the fireworks as they were above the roof-line of the restaurant from our vantage point. There were also about 4 tables between us and the MK window and everyone stood up at their tables to watch the show, which further marred our view. If I had to do it all over again, I'd make the PS for about 15 minutes after the starting time of the fireworks and go watch them outside on the observation deck/waiting area. The view looked a lot better out there.
As for the starting time, you won't be sure about it until less than a month ahead of time. They're adjusting the park hours a lot lately and don't be surprised if they push back the fireworks from the times posted now for your visit. I had the "perfect" PS time for our visit, and then they pushed the fireworks back 60 minutes about 3 weeks before we arrived. I had to reschedule the PS and didn't get the time I wanted.