DUH!!! Yes, it's 20%.
If you have a voucher, you can get the DDE card before you get to WDW I believe. But, if you wait until you get to WDW to get the AP, then you will have to call DDE and order it right away. It can take until the end of the business day before you can pick up the temp. card, or letter. And remember, the DDE office is only open 9-5, Mon-Fri...so if you arrive on a Sat you're out of luck until Mon afternoon.