I use to do this type of cardio several years ago (or 20 lbs ago, lol) and when the weather was good I'd go to the high school track and sprint the straights and recover walk the ends and my routine took about 35 min to complete and on bad weather days I did it on the treadmill.
In those days I had lost the bulk of my weight and had started strength training and I felt pretty good and then I got the idea that I wanted to gain more muscle mass......so I did and now at 5'6" I am at 200lbs and though I did reach my 2013 goal of wider shoulders and a thick back I need to lose 20lbs of FAT! Hahahahahahaha!!!! The fat I have actually helped me get to my goal because of the punishment my body took lifting heavy and so now, it's time to "cut".
High Intensity Interval Training worked before and it'll work again. The basic concept is that up to several hours after I'm done doing it my body is still burning fat go here to find out more:
en.wikipedia.org/wiki/High-intensity_inter
val_training Question: Have you ever heard of this or are currently doing this type of cardio?