You have up to 72 hours before check-in to make changes to your dining plan. I have gone on 2-week trips with different dining plans for each week. What you have to do is make different reservations for the period you want each dining plan. You need to purchase tickets for both dining packages -- 1-day base tickets for paid dining and 2-day base tickets for free dining. I bought 10-day tickets with my first reservation to cover my entire trip. The 1-day tickets I got with my second reservation, I took home and will use them another time and upgrade them. You are also allowed to sell unused tickets.