The 7 minute workout is for people who want to feel like they are working out with minimal effort. It's kind of ridiculous. I tried this for a few weeks 4 times a week and saw/felt almost no benefit. Then I upped it to a 30 minute workout using the same set of exercises and saw quite a bit of progress. That's really the difference. You need your heart-rate pumping for 30 minutes to really see benefits from this, not…
I'm a twig who eats averagely and does no exercise other than walking everywhere (around an hour a day) -- I break a sweat after ~3 minutes and collapse on the floor panting at the end of the 7 >_>
I'm pretty sure that it is helping, because now I can actually do the full 7 minutes, where a few months ago I would only manage ~20 seconds of activity out of each 30-second burst before I fell over from muscle pain.
Are you sure that the specific numbers of minutes are what's important? I am by no means an expert, but I was hoping that "push every group of muscles to their limit every day" would be enough...