the resort category you are staying at determines the line of "credit" disney extends to you. $500 at a value, $1000 at Mods and $1500 at Deluxe/DVC. You can call to front desk and ask them to charge down to your card at any time, call into guest services at any time and pay down with cash, or if you keep it building until check out without reaching your limit, your card will be charged on check out day.
We stay for an extended time coming from the UK and usually once a week, I will get a print out of charges to ensure all is ok, and usually pay down with cash at that time.