This is actually incredibly easy with the turbo speed mode activated. Gameplay runs faster, but the clock runs at the normal pace.
If you're familiar with the game then all you need to do is reach the last room in Memoria where you battle Lich before the game timer reaches 12 hours.
I got this in about 8 hours on my first playthrough with the turbo speed mode on. If you're familiar with the game then it is a breeze.
The item is a hidden pickup in the last room in the right corner.