i think its not by how long they play its by the seriousness they treat it in game

a causual gamer play as when he likes when he feel like killing a monster and logoff or just play till they are bored

a hardcare gamer play like there is no tommorow, even the grind is crazy or how tired they are. They will still continue even there are tons of meteorite falling, they usually set high expectations and aim in the game like getting 10 level up by today if not they cannot sleep or eat lol