How to adjust time for pineapple casserole and pork roast
Don't bother to adjust for the pineapple. You are overcooking it anyway, so it doesn't matter for how long you overcook it. It will still be good. 

The time needed will be determined by the pork, and this depends on the cut you are using. If you are using roast meat, then the time you need has nothing to do with how long the whole roast takes - it depends mostly on the geometry of the cut. You should just stick a thermometer into a piece of pork in the middle and cook to about 60 degrees celsius. (It actually takes a bit more of that, but the meat continues to cook for several minutes out of the oven). If you don't have a thermometer, there is no way to predict the time, it can vary from half an hour to several hours depending on the shape and material of your dish and the amount you are baking. Just take out a piece, cut it open, and return it if it is not ready. If you overbake it, it will be unpleasantly tough. 

If you are using stew meat, it is easier. Leave it in for 3 to 6 hours, the longer the better.