If you can do 20 min at a time...thats what I would stick with, and try to do it 2 to 3 times a day. In the am, lunch break, and after work.....It doesn't all have to be done at the gym to be useful...walk at home, go bike riding, jogging, trampoline, jump rope...anything that gets your heart rate up.....I know it sounds like a pain in the ass, but it should work!