I am going to assume that you mean WHEY protein and not casein. Since Whey is a fast acting protein, there is 2 ideal time to take it. One is in the morning to kick start your protein synthesis and other time is post workout to saturate the body with protein again. Rest of the time, eat slow digesting protein like casein or chicken breast or fish or steak.
On day off, I would take it for breakfast. In a full day, try to consume 1g of protein per body weight.