Hi Scott, and welcome to the Disney Parks Moms Panel!
I think you have a great idea in taking a day off in the middle of your vacation to visit the beach. My family has done this many times, as we have family on both sides who live on the Gulf Coast. It is a great way to put some rest and relaxation into a busy park touring agenda, so you return recharged and excited to head back to the Theme Parks.
Fortunately, I have good news. If you plan on taking a day off to enjoy the beach, you are most certainly able to only purchase 6 Day
Walt Disney World Theme Park Tickets. Once your tickets are activated (on their first day of use) you will then have 14 days before your ticket and any remaining admission associated with the tickets expire. Therefore, you are certainly free to take as many days off from Theme Park touring as you would like, so long as all 6 days of admission are used in full within 14 days. Also, if you later decide to add a 7th day, you can do that as well!
Another option you may wish to consider when purchasing your Theme Park Tickets is adding Park Hopper privileges. This allows you to tour two (or more) Theme Parks each day. My family puts our Park Hopping privileges to good use each trip as we normally start our days in one Theme Park and close the evening in another. This allows us to take full advantage of
Extra Magic Hours offered to select Walt Disney World Resort hotel guests, as well as the regular Park Hours schedules, by planning our touring to maximize our time in the Parks.
Scott, I hope this information is helpful. Please let us know if you have any other questions as you continue planning your trip. We are here to help and want you to have the best possible upcoming Disney vacation!
Magically Yours,
Trish