During weight training your muscles use stored carbohydrates; immediately after your workout your body is looking to replenish those. Ideally you want to have your post workout nutrition within a 30-minute window after your workout session, but up to hour is sufficient. Try to get 30-40g of Whey Protein and 10-15 minutes later a normal Gatorade to provide a good amount of sugar. This combination will refuel your body and aid to grow muscle