That's a difficult question to answer, since everyone's interests are different. If you want to see and do all of Future World in a half day, then I would say it's not going to work. One could easily spend hours just in Innoventions and Wonders of Life alone, and Universe of Energy takes a full 45 minutes from start to finish.
If you are limited to that time frame, I would recommend that you identify the attractions you really want to see and concentrate on those. It will save time if you eat in the park as opposed to leaving for Beaches & Cream.
Getting back to the Polynesian should take 20-30 minutes by monorail.