The duration of each cardio workout varies from individual to individual but eventually you want to get to the point where you can go continuously for a minimum of 30 minutes.  Don’t be discouraged if you are a beginner.  As in anything else a beginner needs to establish a strong base before even attempting to go 5 minutes.  You want to be in your moderate intensity level for at least a few weeks before entering a higher intensity level.

I remember my sophomore year in college when I first attempted to run a mile.  Having always weighed less than 100 pounds, at age twenty I found myself carrying around an extra 15 pounds.  I had spent the summer in Mexico as a foreign exchange student and must have had way too many tortillas!  I went to the track and figured I could run a couple of miles - wrong! I couldn’t even go a quarter of a mile without wheezing and spitting.  I was determined to learn to run and the next day I did go a whole quarter of a mile.  That was my base from which to start from.  It was a slow process but eventually I was running 10 miles and I had lost the extra weight along the way.

If your goal is fat loss, 30-45 minutes per session is what you want to strive for.  In order to avoid over training, 60 minutes should be the maximum.  If you are training for a certain event, or you have reached a plateau, you can exercise more than 60 minutes in a given day but you should break it up between morning and afternoon or night; perhaps you could go 35-45 in the morning and repeat that in the afternoon.  This is of course provided that you have been at the 60-minute mark for some time.  Keep in mind that you don’t need over-kill in your workout program.  If you have reached your goals, and are happy at 30 minutes, stay there.  Remember, it’s your ride.