Hi Merideth,
Thanks for visiting the Disney Parks Moms Panel with your question.
The number of days of a Disney Dining Plan is equal to the number of nights that you are staying at the resort. If you are checking in on a Monday and checking out on Friday, which is four nights, you will receive dining credits for four days. That's good news for you! Credits on the Disney Dining Plan are valid from the moment you check in until 11:59 p.m. on your check-out day. In the scenario above, even in you check in late on Monday and are unable to use any dining credits on Monday, you can use them all day on Friday.
If you are concerned about using all of your dining credits but want to add the Disney Dining Plan, consider going to some meals that require two table-service credits. Disney's Signature Dining restaurants, as well as dinner shows, require two table-service credits. A great
explanation of Disney's Dining Plans can be found online. There are links for brochures about each of Disney's Dining Plans which include information on which restaurants require two table-service credits. If you are concerned about using all of your snack credits, a great idea is to stock up on non-perishable snacks and drinks for your trip home on the last day of your trip.
The easiest way to add the Disney Dining Plan to a Disney Vacation Club reservation which you have made using your Disney Vacation Club points is to call Disney Vacation Club Member Services at 1-800-800-9800. Be sure to do so at least 48 hours in advance of your check-in day, and be aware that you must pay for it in full using a credit card - you cannot use Disney Vacation Club points for the Disney Dining Plan.
I hope that this information helps, Merideth! Please do not hesitate to ask if you have any further questions in planning your trip.