Hi Stephanee - you can get a schedule of May park hours, including extra magic hours, now. Just
click here, and input the first date of your trip. The calendar is sorted by park, so you'll have to scan each section to see where the magic hours are.
As for the dining plan, you pay a specified rate per person per day, to get meal "credits". With the standard plan, you receive one snack credit, one table service credit, and one quick service meal per person per day. In my experience, it does offer value. Our family always saves money when we get the meal plan. The key is to make sure that you use all of the credits.
I hope that helps! Have a great vacation!