I am going to be on that cruise too. This will be my second time on board the Dawn. It was great last year. I am going to start a roll call to see if anyone else is going to be on board.
As 525600 said, the taxis are right at the end off the pier. I would say that the walk on the pier is at the most .5 miles. Hope this isn't too far. If it is, you might be able to get some to help you with a wheelchair. Not sure about that though.
Go to www.dolphinswims.com
. It sounds like the same excursion as the ship offers. The encounter is $75. There is also a Swim with the Dolphins, which is $145. You would probably want to check with them to make sure the tour would be done before 2:00 if you do it on your own.