I have been commuting to work for a while now. Originally it was on my mtn bike and took about 40 min. A couple months later, I was down to <30 min. I just picked up a used road bike and now it's even shorter. I often hear 30 minutes cited as this magic number where anything shorter than that just isn't cardiovascular exercise. Since my goal is to lose weight, should I find a longer route to/from work that will take a full 30+ minutes?
Also, why 30 min?