There's some question as to exactly what is the latest time you can change/cancel a reservation and not be charged the $10 per person penalty. This is from the FAQs on the Disney webpage, but the phone lines close at 10:00PM so the 11:59 is probably online. Also, there are some meals/events that have a different cancellation deadline (e.g. the Wishes Dessert party, CRT, dinner shows, etc) so be sure to read the info on all of your confirmation emails.
From the FAQs:
Q.
How can I cancel my dining reservation, and how much notice do I need to give when I make a cancellation?
A.
You can cancel your dining reservation online or by calling (407) WDW-DINE or (407) 939-3463 up to 11:59 PM Eastern Time on the day before your arrival. Guests under 18 years of age must have parent or guardian permission to call.
Some restaurants may charge a fee for cancellations or no shows. Each restaurant at Walt Disney World Resort maintains its own cancellation policy, so be sure to check the policy when you are making your reservation.
For more information, please refer to the cancellation policy provided in your email confirmation.
