Also, if you go to
www.disneycruise.com, then click on Cruise and Destinations, then click Port Adventures, then select Nassau, Bahamas from the drop down menu on the far right hand side, you can click on the Blue Lagoon trips.
After calling
Disney Cruise, they told me I had the choice of two times in March, 9:30 or 12:45 for both the Dolphin Swim and the Sea Lion Encounters. They said they also have a 2:30 time rarely offered, if the ship is staying later at the port.
Technically, it would work to do both, provided they are not both sold out, but you would not be able to do anything else, such as Atlantis.
Also, you can book directly with Blue Lagoon dolphin encounters at their website or by phone, just do not mention you are with
DCL, otherwise, they will state that they have signed a contract with Disney stating that they will not book any of their cruisers. If you simply call and do not mention the ship you are coming from, they can give you a discount for doing one or both of their encounters. They also mentioned on the phone that they give most of their spots to DCL anyway, so your best chances, according to them, is to book with Disney.
I hope this helps. When we were able to book at our 75 days out (first time cruisers, here), they had some available times for both the swim and the encounter, but we decided to go to Atlantis instead, and experience these on another cruise

. Happy Sailing and I hope this helped somewhat.