When is the optimal time to have a protein shake after a workout? i've read 15-45 minutes following a workout. is 0-15 minutes not optimal?

After cooled down: After intensive/extrenuous exercise, your body/muscles need to get oxygen/nutrients back (they are used during working out) and plenty of blood flow is essential to reduce Lactic Acid build up/cramps etc..During exercise, blood is pulled away from intestines/stomache and supply your muscles. So, let your body recover/normalize the flow, then you can eat--i would say 20-30min is adequate. Good luck.