"In studying the programs of previous Champions, I'm increasingly convinced that extra aerobic activity has been helpful to many of them. The weight training is also a must. You have to understand that a great deal of aerobics may reduce your muscle gains somewhat, but as long as you're doing the weight training, and following the nutritional aspect of the program, you won't lose muscle mass. So in the short term, more aerobics will lead to greater fat loss, since the extra calories you burn will probably exceed what the new muscle would have burned anyway. In the long term, muscle gains are essential, because that will keep you burning calories even when you're not working out. As Bill Phillips writes, "building muscle is a long-term solution to being overly fat." I completely agree.
If you do add more aerobics, my own recommendation is to use the high intensity 20 minute pattern no more than three times a week. You can do more aerobics at lower intensity, but too much of the high intensity cardio will bonk your energy and compromise your recovery. A mild tweak would be to do the 20-minutes at high intensity, and to add up to 10 minutes of moderate level 6-7 activity to the end of each. A more significant tweak would add yet a fourth 30-40 minute moderate session (no high points) on your free day. And the maximum tweak would be to do three 20-minute sessions at high intensity, adding up to 20 moderate minutes to the end (40 minutes total), and then add an additional 30-40 minute session on the free day at moderate intensity throughout. And get plenty of rest. That maximum tweak will trade off muscle gains for fat loss, so it's not something you want to do over the long-term.
Understand that it's extremely easy to undo any benefit from extra aerobics if you let your caloric intake creep up. So be disciplined in the nutrition part of your program as well. Clearly, if the "tweaking" is leaving you constantly wiped out, and you stop looking forward to your workouts, you need more recovery. You can tweak, but don't overtrain. You know you're overtraining if your performance (lifting ability, endurance) declines noticeably for several days in a row. If that happens, get more rest. It's that simple."