Good muscle pumps are the most important element to muscle growth and fat burning. What is a muscle pump? A good muscle pump involves bringing blood to the muscle from peak contractions during exercise. When you picture a pump, picture pumping air into a tire. When it is full, you take the pump loose and ride off. When a good muscle pump is achieved, it's time to back off. Pumping more and more ceases to be helpful and can begin to impede progress.
When pumping blood into the muscle you are bringing the nutrients from your food, hormones and whatever supplements you are taking to the targeted muscle. At that point, you need to allow the blood to remain in the muscle to encourage growth, healing and fat burning. This is where diet meets training- the better the nutrients are in your blood, the better pumps and better results you will see.
Your main objective when training the targeted muscle is a good pump. The faster you achieve a pump the sooner you can be done training that particular muscle. This is why I encourage controlled, specific movements and super sets to achieve a pump quickly and the more precision you use in your movements, the better you can target the muscles you're desiring to shape and tone.
To summarize- eat well, train with precision and speed for quick results, and get home! It's not the quantity of time, it's the quality that produces results.