The standard is to allow 60-90 minutes for character meals, and that's if you want to be sure to meet all the characters. But if you want to be out of there by park open and go straight to KS, you can. I don't think you should need a FP if you go right there at opening. It's really up to you and how much time you think you need to eat, but it seems like at park open everyone heads to Pandora these days and the rest of the park is easy to navigate.