Hi there! I'll fill you in on my experience.
When I called to make my ADR for our upcoming trip, we were not sure if we would be adding the dining plan or not. So the CM said since it was not added on our plan (we are DVC) that she would need a cc# and the full amount was going to be charged right then and there. She said if we decided to add the
DDP to just call back and they would refund us the charge.
So 90-something dollars were charged to our cc on that day. I checked our account online to verify that it went through.
After discussing the DDP with my husband for a few days we decided to go ahead and add it (but being DVC members we don't pay for it until we check in). So I called the Dining line back and notified them we would be adding the DDP. They credited our cc for the full amount that day (again, I checked our account online to verify).
When speaking with the ADR CM, she did say that some places take a cc# to hold/guarantee your spot and that nothing is charged unless you fail to cancel or not show up. But some places (like CRT) will charge your card in full at the time of reservations and the only way to get your money back is if you call and cancel within the cancellation period.
I hope that helps!
ps - this is for our trip coming up in Feb.