Your diet should stay the same regardless if its a workout day or not. Perhaps on non-workout days you may want to eat your protein instead of having too much of it coming from protein shakes. For example, on workout days I usually take 2 scoops of protein powder and on non-workout days I only take one, but regardless I still consume 210g-225 of protein. I don't think it really matters when you take your protein on non-workout days. I usually take one scoop in the morning or afternoon, but I've never taken it at night. On workout days one before and one after workout.