  You will first want to preheat your oven to 450 degrees. Cook the roast for 10 minutes then reduce the heat to 250 degrees. You in all will want to bake the roast for 90 … minutes in total including the 10 minutes of high temperature cooking.reheat your oven to 160°C (325°F) and use these cooking times to prepare a roast that's moist, tender and delicious.Your roast should be covered with foil for the first hal … f of the roasting time. 4 to 5lb Joint 20 minutes per pound in weight plus 20 minutes extra. 80 minutes total.