Okay, found my old itinerary from July 2007. We had a 5:55 pm ADR for 1800 Park Fare and then Wishes was at 9:00 pm that night. We were a party of 10with 3 kids and I remember we finished a leisurely dinner and had at least 30 minutes until we had to check into the marina. Our marina was at GF so we didn't have to travel to another resort. I remember the wait because my FIL was irritated about it....sigh, can't please everyone. Not going to try next time.
You can call (407) WDW-PLAY and find out a general time when you have to check in for a 8:00 pm Wishes cruise and then change your ADR time accordingly.
Have fun!!!