I am not sure why restricting the players play time is a good method for bringing money. I suggest you get rid of energy all together so that more players can actually play the game longer and have more chances and reason to buy something with money. Or shift energy so it doesn't affect the amount of game play but the amount of rewards.
In any case, creating a system that only allows customers to enjoy the product for approx 2 hours is probably not the best way to earn loyal customers. More game time = more money.
Well you could start creating alt-accounts, though you need to pay some money for it, you permanently get increased mist energy (though you'll have to get equip for several characters.)