The third level of mediation is choice-less with no-thing to do. No object of your focus (as opposed to the nose in level 1 and the body in level 2). It is level 3 for a reason. It is hard to not have an object of focus and not have your mind take over with thoughts of past/present/future.
This is why you must first learn to sit your mind with the use of level 1 to form concentration and level 2 to de-program/condition with neutrality. Once de-conditioned and with strong neutrality, choice-less awareness is a little easier. Sit and be still.