4 hours is the amount of time it takes for bacteria and virus' to multiply to dangerous levels in a perfect storm of bad conditions. of course, it may be ok to do it well before and leave it out, but that is certainly causing a potential hazard. say it got contaminated during that time, then it can really make someone sick. that is why we take many precautions to limit potential hazards... say it got contaminated and you cooked it right away after taking it out of the refrigerator, it would likely be fine. the 4 hour thing applies to all potentially hazardous foods. of course, the 4 hours can start from the meat supplier to your restaurant to the plate, so again it is really important to be as cautious as possible.