Do the 20-minute program, and add on the following 10-minute routine. Repeat the full circuit one or two more times. You'll need 3- to 8-pound weights.
Lie on back, with hands clasped behind head. Lift shoulders up and bring left knee to chest, extend right leg out, and twist right elbow to left knee. Repeat on the other side. Keep alternating until you've done 8 to 10 on each side.
Mix in some cardio. Once you get in the groove of the strength routine, try to work in some aerobic exercise on your off days. Start small (a brisk 10-minute walk) and build from there. Finding the time is easy once you begin seeing and feeling the results!