High intensity exercise can be more aerobically beneficial than traditional, steady state, low intensity exercise such as jogging or aerobic classes.  

Many people are encouraged to perform aerobic exercise to improve their heart and lung function.  But during the recovery from high intensity exercise is when the body is getting the most stimulation of the aerobic system. As one recovers from this type of muscular activity, lactate (an anaerobic by product), begins to accumulate. The cells begin to process this lactate by converting it into another chemical that is metabolized by the cell aerobically. If one is intent on improving their aerobic capacity, it is important to understand that the aerobic system performs at its highest level when recovering from lactic acidosis (the lactic acid burn.)

So, if you are looking for your best results in a fraction of the time,  put more effort into your workouts, not more time.