When you mentioned 'opening it' I was wondering - is this the sort of thing that comes in one of those tins with the key? If so, it's probably preserved into the next millenium so you have lots of time. 
If it's a regular fresh or smoked ham, you probably still have several days on it, if stored properly. You know how I am about storing food!
Such a neurotic.
I purchase the Kansas City hams because I really like them. But they come vacuum sealed already (perfect for me!) and frozen. I usually take it out of the freezer 2-3 days ahead of time, obviously, so it can thaw before preparing and putting in the oven. But we can eat off of that for quite a few days after and it's still perfectly good (stored in the refrigerator in Lock & Lock).