I completely agree. I feel the lack of know limit and the fact that it only effects him at midnight. If you are dead set on keeping it a time based thing then maybe he has a 10 min timer before the gravity backlash. Or you could have it be like a muscle and get tired after exerting force the time being dictated by how much force or for how long he is applying force. It's a cool quirk but the seemingly limitless power of it seem a tad OP in my opinion.