Cindy's - they take full payment on your credit card when you make your ADR. If you have your DDE card - they will give you the 20% off.
IF you do NOT have your DDE card when you make the Cindy ADR - then once you receive your DDE card - call WDW Dining and receive the 20% discount credited to your credit card.
Do this before going to Cindy's. I think at the podium, it will be too confusing to get your 20% back.
You could even call WDW Dining at WDW before going to Cindy's at WDW - once you get your paper DDE at EPCOT guest relations. Just do the 20% credit through WDW Dining - not Cindy's drectly.