In my opinion and experience training clients, no workout, in its entirety, should ever exceed an hour for just about any goal type. In terms of the high intensity exercise we seem to be talking about in the traditional workout style, More does not necessarily always equal More, as in more input does not always equal more output in terms of gains. Our inputs only make gains up to a certain maximum and, if we continue that same path past the optimum/maximum point, our inputs give us less and less gain.
As Pavel Tsatsouline, one of the premiere fitness and strength minds on the planet says in his book with Dan John "Easy Strength," "The more you push on the limits of your body, the more your body pushes back." You can talk to anyone who 'lives on the edge' with their fitness...Yeah they may look great, but look under the hood and you will find a shriveled up, miserable, over-trained human being. I find a program of 2 days of about 30 minutes of sprints or metabolic work (even as low as 15 minutes has proven effective), 4-5 days heavy, low rep strength training at about an hour with warmup, and as much low level aerobic activity as possible is premiere for all goal types.