Is it a one-time pill effect or a power you gain? Do you stay looking however you did 10 hours ago forever?
If it’s a power, let’s say you use it immediately twice in a row. First time: boom. 10 hours younger. Second time: does nothing happen or do you then look 10 hours younger than then how you currently appear? So you look 20 hours younger. Could you keep spamming it indefinitely until you very slowly reach any age you want?
I suppose that depends on whether it makes you look 10 hours younger than you ARE or 10 hours younger than you CURRENTLY APPEAR.