Yes. Be at the bus stop about 90 minutes in advance. (You should be at the restaurant 10 minutes in advance.)
If, on the way from the Magic Kingdom bus station to the monorail station you find the small boat (as opposed to the big parking lot ferry) for Grand Floridian at the dock, take that instead of the monorail. It's more direct but the wait is longer if you just miss one. Don't confuse the Grand Floridian boat with the Wilderness Lodge boat which shares that dock.
(Perhaps 45 minutes in advance if you take a taxi all the way from All Stars to Grand Floridian.)