I would not soak a snake for 30 mins, that's a long time to stress a snake by forcing it to be in the water that will cool down in that time and you'll remove a lot of the snakes natural oils that help it shed. Just up the humidity in the tank and the small patch of skin should come off on its own, if you want if it's still there a few days after upped humidity you can gently rub the skin with a wet wash cloth.