Snow White, Dopey and Grumpy roam around. No rhyme or reason to when they will get to your table. The could be at a table right next to yours, then take a break and when they go back, they are at the other side of the restaurant! CMs do know more or less when you arrived and make sure they will get to you mostly within an hour.
Something different with Storybook compared to other character meals is that.....
1) Every 20 minutes or so, a voice will come over the loud speaker announcing a special dance by Snow White and the dwarfs and they dance around the restaurant. Everyone is welcome to join in the dance, by their table...its not a march around like Akershus or Ohana breakfast.
2) To get a photo op with the evil queen, you are, at some point, summoned to go visit her at a specific location in the restaurant. Just as the fork is about to enter your mouth, you could be summoned and you MUST obey her wishes!
So basically, there is no real down time at dinner.