I'm fairly certain it is 45 days from leaving. We are going 9/23-9/30 and ours is due fairly soon. Yep, just read the fine print on the back of the confirmation letter- Final payment should be sent to Walt Disney Travel Co., Inc. P.O. Box 10375, Lake Buena Vista, FL 32830- I'm assuming you can just call them as well and give them a credit card number- I can't read a penalty for paying late- but I do see where there is a cancellation fee of $100 and a change fee of $50 if you do so after that 45 day period. Hope this helps!
Tara.