If it is a country ham, meaning salt-cured then you need to boil the salt out of it. I may get flamed for this, but that article is not how I process my ham. So here is what I do.
I get a lard tin, I usually have to cut off the hock to make the ham fit but since yours is split you may not have to. If it is not a salt cured ham, and is a city ham it may not be fit to eat if you do this, you could make ham soup maybe.
Anyway put the ham in the tin fill it full of water bring it up to a boil let it boil for about fifteen minutes then bring the heat down to medium-low for about 1/2 an hour then let it cool down enough so you can take it off the stove, but just barely cool enough. While it is cooling down get blankets and spread them out on the floor, one or two thin ones should do, then get some newspaper and spread that in the middle of the blankets put the tin in the middle of the newspaper and wrap the tin with the newspaper then wrap the blankets around it and then push it over into a corner overnight.
The next morning pull the ham out of the water give it a rinse and pat it dry, it will still be warm-to-hot. (I rotisserie ham hocks and small hams I get from my butcher but I have never done a full size ham I would imagine the amount of drippings would make a mess though.) Next I get my big roasting pan put the ham in it and pat it down with brown sugar, medium or dark is up to you. Then I cover it with aluminum foil, making sure I tent the foil so it doesn't touch the ham, and let it cook usually between four and five hours for a good size ham at about 325. The last half hour I take off the aluminum foil and if I feel it is necessary I add more brown sugar and let it caramelize.
I have been cooking ham this way for as long as I have been cooking and the process is passed down from my mother and her father before her. Farther back than that I cannot confirm or deny. :)
Here is a great article on country hams and other hams, just to make sure you do have a country ham, and gives other great suggestions on how to cook a ham, although they do it differently than I do.
http://www.amazingribs.com/recipes/porknography/zen_of_ham.html
Best Answer
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.