Cooking time

If this is a braised roast, such as in a covered dutch oven with liquid halfway or so up the sides, your cooking time should be lengthened, maybe half again, but not doubled. Does your recipe tell you what to look for when done, such as meat should be easily pierced or almost falling apart? If so I would cook for original suggested time, see how done and proceed from there. If you are trying to time other dishes to be done, a braised roast is pretty forgiving and can sit in its liquid for a while while other dishes are finishing cooking. If your recipe is for a true oven roast, such as you'd do for a standing rib roast, maybe check times for a boneless rib roast on the internet and work from there.