Hi, Trisha!
What a great planner you are, sharing your wisdom with your sister as you plan a great vacation together! Well done!
For information regarding Walt Disney World
Extra Magic Hours, take a look at the link I included here. You'll find the perks of using Extra Magic Hours as well as other useful specifics and tips, too.
In short, let your sister know that planning your days around Extra Magic Hours often results in Guests enjoying their tours in the parks with lighter crowds. In the mornings, we use EMH to get in to our favorite attractions before the rest of the park Guests have even entered the park. Evening EMH ensure that we can enjoy our favorites long after the regular crowds have gone home. We love it!
If that link doesn't work for you, please let me know; also, feel free to send me another question which includes your dates of stay and the WDW Resort you're choosing for your upcoming visit. I'd love to help you make the most of your vacation, Trisha...including use of Extra Magic Hours!