I have a couple of quick eaters and then I have two very slow eaters. They have approximately half an hour for lunch. Once it's done, whether they are finished or not, i pick up the plates. Then we do a story time and it's nap. I don't allow any of them to sit there any longer to finish their food. Same at snack time, they don't get to sit there and take as long as they want to eat.

Don't worry they won't starve.