It is a common misconception that the more time you spend in the gym, the faster the desired results will come. More is not always better and ignoring this concept will lead to over-training, the act of working one muscle or a group of muscles beyond what is needed to cause stimulus for growth. It is also called over-straining. Over-training is also the number one reason people do not progress in muscle and lean tissue development. Even professional body-builders suffer from over-training and fail to progress.
Instead of focusing the number of sets, think about the quality of the set or sets of exercises. If you want to make the most of your potential then avoid over-training at all costs. Overdoing high-intensity workouts, either by executing them too long or too many sets, will get you injured. Your muscles may even shrink due to the stress of over-straining which causes a hormonal condition that turns muscles into fuel to protect the body from the additional stress.
You must let your muscles heal before your next work out. Recuperation allows for you to exercise smarter and protect your body from injury. Without the proper rest you will not achieve your desired results.