It's not so much the hours, as the motivation. If you do everything else you need to do (such as work, chores, going out with friends/girlfriend, other hobbies) and you have spare time, and you spend that on games, well then you're a casual gamer. It doesn't really matter how many hours that is, some people just have more excess time than others. People who game first and do the other things later, are more like hardcore gamers. That said, there are plenty in between like me, who set aside a set amount of time for the things that need to do, and play the rest of the time. I still get done what I need to do, but I pretty much set aside some time for games aswell, not just the excess time I have left over after I've done everything else.