Disney charges your credit card at the time of your payment, just as occurs with any other purchase; however, when you pay for Disney purchases can vary.
Disney store purchases - charged at time of purchase
Disney vacation packages - You will pay a deposit at the time of booking and can then make deposits online or via phone leading up to your trip. Your vacation package balance is due 30 days before your trip
Disney room-only reservations - You'll pay the remaining balance at the time of check-in. Additionally, Disney will place an initial $100 hold on your card for estimated hotel incidentals during your stay
Disney's own site does a nice job of clearing up payment questions in their FAQ.