We did this in September. We met on the ship at about 9:45, I think. Check in took a bit of time. As I recall, it was a short, guided walk from the ship to the boat that takes you to the lagoon. That boat ride was maybe 30-40 minutes? You got to see some of the lovely homes on the shores of Nassau, which was nice, but otherwise, its just a boat ride.
Once at the lagoon, we had a 15 minute educational presentation before heading down to the dolphin area. We were broken into two groups of about 6 or 7 people each and each group had its own dolphin and trainer. We were down in the water on a raised platform most of the time, interacting with the dolphin. We were not doing the "swim" just the "encounter." We got to pet it, dance with it, feel its teeth, feed it fish, hug it, get a kiss, have a picture, etc. Each person got to have their turn, so we were probably in the water a total of 45 minutes start to finish. It was really fun. After that, we had time to shower and change (nice showers, btw), have a snack, shop and play at the beach for a bit before we caught the first boat back, so maybe an hour or so of "free time"? Just guessing. I wasn't wearing a watch (can you tell?).
My 3 year old and I had a blast. I was really pleased with the amount of interaction and she was thrilled. We bought the DVD and she still loves to watch it.