Maybe you have heard about interval training. For maximum cardio benefits it is the idea that instead of running or cycling for an hour at a steady pace, you should go for much less time using bursts of high intensity speeds for a only a few minutes. For example cycle at a warm up pace for 3 minutes then push the speed up and cycle to almost your max for a minute or two. Then reduce and repeat. Cut the lower level speed to recover each time then hit it hard.
It is said that too many laps, miles, hours etc, can be so hard on our bodies that you are defeating your purpose and not gaining any benefit. Many runners hit mile after mile, when they are abusing themselves and not gaining any healthy benefit. With less miles and much more intense short bursts of speed they can gain more in overall health and work less.
Its not the amount of time spent its how you spend it.
My 30-40 minute strength training work out is more intense and does more for the body then multiple set much longer workouts.It is a fact and can save you time and get you more and better results that are visible.