20 – 30 minutes per pound is the approximate cooking time for a roast – but you have yourself one mighty big roast! Just be sure to use a meat thermometer for an accurate temperature. Check the thermometer by peeking in the window of the oven rather than continually opening the oven door.lways position the pork roast in the pan so that fat side is on the top. Measure one tablespoon of olive oil in a small dish. Add 1 Tablespoon of dried spices to the oil. You can use rosemary, sage, thyme, or oregano; or a combination of these that equal 1 tablespoon.