i cook for longer than that, but we have a dodgy oven at the moment - have never had it dry out though. a lot of it is instinct based when you're cooking a roast - every oven is different, so it's only a guide - if you have an oven that seems to cook to the time of most recipes, it shouldbe ok to go by the guides given, but if it cooks fast or slow, you will have to adjust to that. i find that sticking a big fork into the middle of the meat to check that it's done right through (clear liquid comes out, not bloody) - i tend to stab to the bone

we also put about a glass of water in the bottom of the pan (we dont' cover it) and make sure there is moisture there all the time