Depending on the type of food usually 1-2 hrs before. It ultimately depends ont he person. SOme people can eat right beofre the game and be fine. I recommend my players to carb up about 1 hour to 1 1/2 hours before kick off.
No, they shouldn't snack before the game....they should eat a meal before the game. 6 hours is way too long to go without eating. Two hours prior to the game is about right for a full meal. As the game approaches eat smaller snacks. Players should eat whatever they are accustomed to eating or they risk getting sick.