This is quite an interesting experience. When I am doing yoga breathing (almost exclusively Kundalini), I have no difficulty with holding an inhale for a long period of time, or holding an exhale for a moderate amount of time. But as soon as there's a timer involved (actually, as soon as I'm paying attention to it), as soon as there is the pinching the nose - even before the actual activity, just at the description of the activity or the thought of doing the activity - I go into a a breath panic. With my nose pinched, there's an urge to breathe at about 4 seconds. With my nose not pinched, but still holding my exhale out, the urge starts maybe at 12 seconds. I know I have some trauma over suffocation, so as soon as the awareness of not being allowed to take an inhalation is present, the panic sets in. (I chose to ignore the contraindication of panic, because my curiosity is greater than my sensibility ☺️ and ultimately I know that I'm safe).