I would just put it in the oven for a couple hours and then check it to see how tender it is in two hours. If you need to be gone for three or four hours, just make sure you have plenty of moisture on it and it will be just fine and, once again, depending upon your beef quality and cut, it should be fork-tender when you return. I put mine on around noon to eat that night or early in the morning for lunch. I even cook it one day and serve it the next day. It only gets better with time.
Hope this helps. Write back if you need more info. ----- Barney Chapman