You would need to do it sooner if your charges are close to the limit set for your resort. For Value Resorts, I think that it's $500. Moderate Resorts are $1000 and Deluxes are $1500. If your room charges reach that level, Disney will charge the card that you have on file and then reset your balance to $0. You can get the charges reversed, but it can be a big pain in the butt to do it.