See notes for an overnight option.
Overnight French Toast: You can assemble everything the night before if you like and refrigerate the casserole. After spooning on the apples cover the casserole with plastic wrap and refrigerate it until the next morning. In the morning add the topping and bake as directed. Remember it will take longer to bake it cold. One option is to allow it to come up closer to room temp on the counter but either way plan on more baking time to reach the desired level of doneness.