You don’t need to spend lots of time a the gym to gain the benefits. Depending on your goals, 30 minutes a week may be enough.
From P.D. Mangan:
“Bodybuilders, gyms, and most publications devoted to it advocate that you train often, as frequently as five times a week. Is this necessary, and is this optimal?
The fitness industry has an obvious conflict of interest here: it wants you to use their products as much as possible in order for them to earn more money. If you are told to workout more often, you will be more likely to renew your gym membership, buy more supplements and equipment and magazines, and just generally to order your life so it revolves around weight lifting and fitness.
Others, more scientifically oriented, claim that you don’t need to train as often to maximize muscle gains, not that you need to do more than one set of each exercise. In the very informative book Body by Science, Doug McGuff, M.D. advocates once weekly workouts, a far cry from the three to five a week often advocated elsewhere. McGuff bases his recommendation on a number of things, most importantly the speed at which muscle recovers and grows from an intense workout, which is much slower than most people think.”
Source: Brief Workouts Produce Significant Strength Gains – Rogue Health and Fitness