The Right Answer: If you're trying to maximize muscle growth, (which you are if you are lifting), then you should consume your protein shake within an hour of working out. If you really want to maximize your gains, drink a glass of fruit juice along with it. Or just drink a meal replacement after your workout. There's about a 30-20min window after an intense workout where your body is primed to absorb the protein, and it needs to replenish it's muscle glycogen stores, (hence the fruit juice).
It would be smart to drink at least two protein shakes per day.