Roasting two ham roasts at once
It depends on your oven and how big the hams are. If you try to cram 2 big hams into your oven and it's not a fan oven then you probably need to add extra time. If they are moderate size then it shouldn't make much difference at all. If they are big but you have a fan oven then you shouldn't need to add time. 

The best way to make sure something is done is not by time, but using a meat thermometer. When the ham is 150F at the center of the meat's mass then it is ready to come out, below that it still needs more cooking.