Only did 2 hours of hanging yesterday but damn am I sore. I did 3 back to back sets of 40 minutes with almost no break whatsoever(+5 minutes) and I was so fatigued afterwards. Then I did 10 minutes of edging.
I think the idea is that you want to stretch as much as you can with hanging and manual stretching and then when you are done with your workout, do something that forces a lot of blood to the penis, like clamping, jelqing, edging to fill up the newly expanded tissue with blood. What I usually do is reverse dry jelq for 5 minutes afterwards because all the soreness is on the lower 1/4th or so of my penis, that tissue has been stretched the most and under the most tension and is very tender and sore afterwards.
Basically all I do is get like a 40% erection and then grip my penis near the base and pull the skin as far up the head as I can, then squeeze and push downards to force all the blood into the lower part of my penis.