My husband did this last year. I can't remember exactly what time we actually saw him in the water, but it seemed like it took FOREVER between the time he left and the time we actually saw him in the tank. Kids were getting antsy and the wait was pretty rough. So I know that isn't super helpful on timeline, but I would recommend you get it as close to as possible as when you'd be in the tank because my husband had no timeline so we waited and waited and waited until one kid was in tears, another one was rolling on the floor. LOL It was a long wait.
Adding that we didn't wait at Coral Reef. We waited upstairs by the big windows. I don't know if waiting at a restaurant would have been less painful. By the time we saw him, the kids didn't even care.