I'm not an expert on the topic, but I've gone through a lot of material within the past few months, and these are some of the opinions that I currently hold:
1. The body grows for around 36-48 hours after hitting the gym, provided that the conditions are right (anabolism).
2. Without proper workout nutrition, growth may be delayed for up to 24 hours after leaving the gym (during which the body continues to be in a catabolic state). By proper workout nutrition, I mean at the very least some simple carbs so that the muscles can replenish their glycogen.
3. New muscle mass is created from the proteins you eat. You can't grow more than what you're eating. On average, 100 grams of meat contain 20-30 grams of protein. (There's a limit on how much protein the body can use, so don't go bananas.)
4. Digestion of a meal takes around 3-4 hours, after which you need to eat again, so that the body has the raw materials it needs for growth. (Actually, this isn't entirely true, and depends on what you eat. Casein, for example, takes up to 7 hours to digest.)
5. You cannot really grow without a caloric surplus. Your muscles will become more optimized, and they might look better, but you won't experience any significant growth.
6. Caloric surplus. Caloric surplus. Caloric surplus. Not kidding. Your body uses a
lot of energy just to operate itself. If you're not eating a sufficient amount of calories, you body simply won't have enough energy for muscle growth (which happens to be less important than keeping your brain operational).
For nutrition info, probably the best place to start would be with
John Berardi, particularly the articles section on his website.
For both workout and nutrition info, I know nothing better than
T-Nation.