Protein in the form of a sports supplement such as whey protein, is best taken either;
1) Upon waking - after your body's daily fasting period (i.e. sleep) your body needs nutrients to continue the recovery it constantly seeks from hard training, specifically protein and a fast digesting kind such as whey protein will allow your muscles to recover as quick as possible, minimizing muscular breakdown.
2) Post-workout - immediately after training your body is craving nutrients to assist with recovery following a hard, intense workout and protein is a must in order for our body's to come back stronger. The sooner you can get it in the better and within the first hour after your workout your body will be highly sensitive to the uptake/absorption of these nutrients.
3) Before bed - giving your body a bump of protein before bed can be a wise move to help prevent the chance of muscular breakdown and aid recovery and growth. A Casein or 'Blend' protein would be most appropriate in this case for a more extended release time.