If you have a reason that you need to delay final payment, just mention it to your guide. When I added on last June, I put my down payment at the beginning of June (the day after my statement closing date on my Disney Visa). I then asked if they could wait to charge the balance to the Visa until July 3rd (so it would miss another statement closing date).
Since I was getting 6 months, 0% interest for using the Visa, I wanted to delay things as much as possible. They had no problem and set it up to autobill our credit card. On July 7th, they did and then the contract closed.
It was great because I got until January to pay the whole thing off with no interest (had the money but it was nice not having to part with all of it at once!!!).