Jennifer,
Fantasmic! has a reported 25 minute show duration, and on the 18th it starts at 6:30 pm.
But let's bake a little reality into that pie. So the show ends at roughly 7:00 pm. The crowds, always big ones, will take some time to clear out, with many headed to the park's exit gates. To be conservative in the estimate, let's say you get to the bus depot for the park at 7:30, then wait as long as 30 minutes for a bus. That get's you to 8:00 pm. A half hour bus ride has you arriving at the Polynesian at 8:30 pm.
So is it doable? Yes. And in mid-November (a very slow crowd time), probably very achievable. I would say that this is a good plan you have come up with!
And oddly enough, I actually prefer the Hollywood Brown Derby for lunch over dinner. It is a very posh, delicious dining destination, but I just seem to like the daytime dining. Plus, I try to avoid dining at odd, off-hour times, like 3:30 pm.
Go for it!
Have a magical (and delicious) vacation!