Not really sure what you are asking. Or what you are able to do in the way of swimming. Are you a good swimmer? Have you ever swam for 30 minutes at one time before? Do you have shoulder or neck issues? There are a number of ways to program 30 minutes of swimming. But it sounds like you are going to do other things that are more like your exercise class. If you aren’t goiong to work with an instructor, my advice would be to start small and work up from there. Maybe 5 minutes of extra swimming/exercise at first and add a minute to each session each week. Then work on doing different things after you are swimming the extra 30 minutes. Like some speed work or swim drills.