How much longer do I cook the roast?
Without a thermometer (which I personally do not own), the other way of testing pork to make sure it is sufficiently cooked is to pierce it with a fork or skewer in the thickest part.

Check this extract from recipetips.com:


  Piercing: Another method for testing doneness is to prick the cut of pork with a fork or the tip of a knife and check to see if the juices that escape run clear. If the juices are clear or have just a very faint pink tint, the meat is done. If the juices are not clear, the meat should be returned to the heat source for further cooking.