Photo Credit Diane Shear/Demand Media. Lower heat to 325 F, and continue cooking the pork roast. According to the U.S. Department of Agriculture, you should figure on cooking bone-in pork roasts for 20 to 25 minutes per pound.A 5-pound roast, for example, will need between 100 and 125 minutes of total cooking time, which includes the searing time.hoto Credit Diane Shear/Demand Media. Lower heat to 325 F, and continue cooking the pork roast. According to the U.S. Department of Agriculture, you should figure on cooking bone-in pork roasts for 20 to 25 minutes per pound.