I can two hand dead hang for 1.5 - 2.5 minutes. When I try one arm dead hang I can't stop rotating and swinging, so my time is probably 15 seconds. How can I achieve balance?
I don't see why you would generate swing during the hang, so I have to assume that you start the hang with some swing. In that case, just make sure you don't release your feet from the platform until you've ensured that your body is at equilibrium.
In order to stop rotation, you're going to have to make an effort to counter the rotation. Hanging from one arm will tend to rotate, but you have to just counter it by twisting your arm against it. It's hard at first, but you'll soon enough have trained the relevant muscles to make it easy.
An alternative is to use your free hand to hold onto the frame that holds the bar, or use a rubber band hanging next to you. You don't use it to assist the hold. Only to stop rotating.