Welcome to the Disney Parks Moms Panel, Walter!
Most Walt Disney World® Resort Restaurants offer a thirty minute grace period for
Advanced Dining Reservations. After thirty minutes guests will be considered a "no-show" and subject to the fee of $10.00 per person.
You also have the option of modifying your reservations while on-the-go from the My Disney Experience App on your smartphone! You'll have until midnight the night before your reservation to make any modifications or cancellations on your own.
If you'd like to try to make any day-of modifications, subject to availability, you may stop by the Concierge Desk of your resort hotel, or any Guest Relations window within the theme parks or Disney Springs.
I hope this helps! Please let me know if you have any additional questions, Walter! I am here to help.
Faith