I cook my roast for no less than 24 hours. This cut of meat is very forgiving and really cannot be overcooked. If the liquid cooks down too much, add a cup or so of water. If the top of the roast get a bit dry or crispy looking, I just chop it up with some of the moist inside meat and use it as normal. I feel doing so provides a bit of texture as grilling a piece of meat would.