What are the laws governing mandatory lunch breaks on the job?

There is no federal law regarding timing of lunches or other breaks, or even requiring them at all. Some states have laws regulating this, but you need to say where you live, or check your state website. Even in the states that do have laws, it's usually that you are required to have a break after x amount of time, not that you would have to have worked x time before you get a break. With 3-1/2 hours work before lunch, and 4 after, I doubt that would violate any state's law.