Fast Pass for Frozen Hoilday Wish

I hope to get a fast pass for Frozen Holiday Wish after using my first 3 passes. What does the fast pass get me exactly?
In the event this doesn’t work out, plan B is to get there early enough that we can be close enough to see and hear the stage show portion. What time would you recommend arriving there to get a decent seat. My kid-o really wants to see the characters. Also, where should we sit/stand? By the way we will be there on 12/28 - a level 10 day.

There isn’t a FPP for Frozen holiday wish, or Wishes, or the Parade anymore. For Wishes you need to book the dessert party, and the parade spot is connected to a lunch package at Tony’s, or it was a couple of months ago.