If you are talking about the Dolphin Excursion that you can book directly through
DCL, then yes, the DH and I did it on our cruise.
It doesn't really take that long. To me the longest part was actually meeting with the others who were doing the same excursion and then actually getting over to Blue Lagoon Island where you actually do the Encounter. It takes about 20 minutes or longer to get over to the island, which you will travel on a ferry to get to. Once you get on the island, and get over to the place, it really isn't that long. You do have a brief overview with one of the trainers to go over a short history about dolphins, and what you are about to experience, etc. I would say that takes 15-20 min, but seems like forever because you're so ready to see the dolphins. They actually put you in the water in groups of about 8 or so. We were in the first group to go, so that made our time a little shorter. Everyone else sits on the side and watches until their turn. I would say you probably spend maybe 30 minutes actually in the water with the dolphin. After you get your turn in the water, then you are free to go. You can walk up the steps to the gift shop where you can also purchase the pictures that they take of you and the dolphin. After that, you are pretty much free to explore the island. They will give you a coupon before hand that will get you your lunch there. There are hammocks, so it was nice to eat, and then lay in the hammocks for a while. The ferry returns to the island to start taking people back after a certain time, and then runs every 30 minutes ( I think, but don't quote me on that.)
Everything is pretty easy. Disney has everything arranged, so it's nice. Everyone who is doing that excursion will meet in a designated place at a designated time. A CM will give you all the info and also give you a sticker to help you remember which group you are with. They will also give you a meal ticket, and then lead you off the ship to where you will meet someone who will take you to the ferry and over to Blue Lagoon.
I highly recommend this excursion! The DH and I really, really enjoyed it!
HTH, any more ?'s...ask away!