As the above posters, I like my money best in my pocket than in Disney's.
If you have a savings account, let that money earn you a few pennies while you wait for your balance due date.
If you don't, then you can call as often as you want to make payments.
I know some people prefer to pay in installments. They sometimes fear that, if it's on a savings account, they'd be tempted to use the cash for non vacations related purposes. So they prefer the money be taken from them ASAP
so if you're like that, call them anytime you want to put some money towards payment of your holiday.