How Far in advace to book Dolphin Swim

We are on the Dream in March 2016. I want to do the Dolphin Swim at Chakkanaab park with my kids. We are going over Spring break (I know, one of the busiest times of the year), I have been watching for a good price on the website, how far out should I book the Dolphin Excursion?

I would say get it as soon as you can if you really want to do it. Incases it sell out.

What company are you booking with? Are you going with the cruise line or a private company? I'd love to know who you're going with. Thanks!