We were married in Disney more then 8 years ago but had a timeline similar to yours. We were staying in a DVC studio that one of our guests gifted us for 2 nights so we made sure to have food in our room. Our ceremony was a 9:00 and our reception was from 10:00 to 3:00. When the reception was over our guest were on their own until meeting back up in Epcot for our DP. After our reception we were with our photographer for about another hours taking more photos around the Boardwalk (we were staying there and our reception was at Atlantic Dance Hall). We were so full from brunch and so excited about the whole day I think we were just so busy all day we did not realize what was going on.
I did take off my dress for the few hours in between and yes my DH was very able to get me back into it. A few friends stopped by our room and we all walked over to our DP. We did more pictures at our DP so honestly we did not get to eat many desserts. I would definitely put my dress back on for the DP.
Another thing - you said you are doing a MK shoot the next day. Will your DH be helping you get ready or are you having someone help you. We did our MK shoot a few days after our wedding and yes my DH helped me back into my dress.
I would keep some light snacks in your room if you can or just order room service.