I don't think that the amount of time has to do with being a hardcore gamer. What makes the difference between a hardcore gamer and a casual gamer is the amount we're willing to dive into the game's 'depth.' Say a casual gamer and a hardcore gamer are playing Oblivion. I see the casual gamer as simply playing the various quest to simply be done with the game. The hardcore gamer would take time out to explore the world itself and maybe even learn about it instead of simply focusing on 'go here do thing A.' That may be a bad exampled as that game is made for roaming, but the general idea I'm trying to show is there.