That's only too long if it results in the salt in the rub curing the meat to the point that you get a hammy taste. If there's not much salt in the rub and you haven't experienced this problem, then I'd say that if you like the results you're doing it right. I started this way, experienced the hammy taste, went to rubbing my ribs right before cooking and had a few experiences with less than flavorful meat. Now I'm back to rubbing them the night before in an attempt to get them back to the way I like them. Not sure if it's going to help but that's where I'm at.