open the tin. keep checking. when it gets to the desired humidity, move the tobacco to a glass jar with a good-sealing lid (Mason jar, Ball jar, etc). If you go through tobacco quickly, ie a tin in a week, it isn't necessary. If you're bouncing from one tobacco to another, prolonging the life of that particular tin, it's a far better option than re-humidifying the tobacco over and over again. Personally, I never leave tobacco in the tin for maybe longer than 24 hours after popping it. It's not a battle I enjoy, so I avoid it.