If your into hittin' the gym and working out. Have a protien shake after your workout, like BigH said you have a short window. I also recommend that you take a shake right beforfe you sleep.
Your muscles do most of the repair, the damage you did during excercise, at night. So having protien in your system before you sleep will allow you to feed them. Also, try to eat every 6 hours or less. After six hours w/o food, your body switches to internal sources for energy and protein is the first on the list.....namely your muscles.
GL
Psalm 144(1): Blessed be the Lord my strength which teacheth my hands to war, and my fingers to fight.