Exercising for 30-60 mins does wonders for fat loss/leaning up. Any time after the 20-30 minute point is pulling from fat stores for energy. Up until the 20 min point(assuming a decent heart rate) I think you using glycogen stores(basically carb sugars) if I remember correctly. Been a few years since my college course but I think that's how it works.
I have both a treadmill and stationary bike in my apartment and 60 minutes flys by when you turn on the TV and play a game of Madden or something.
Something like that 5 days a week and it usually doesn't matter what you eat(within reason). You end up burning 3500 calories a day and eating maybe 2500. The weight and fat falls off and you lean up while mostly eating what you want. Avoid alcohol if you plan on sticking with anything. One wasted night and you fall off the wagon for 1-2 days usually.