If you have negative results, split time in half. You can either do 2 sessions with half time, or throw one away completely. That might be individual, but I get small injuries like red dots quite easily even at 5HG and mid time. At the same time in shorter session I can push even up to 15HG and be fine. So in my experience it’s more about duration of session than pressure. When you find optimal time, you can check different pressure. Usually if you have temporary expansion (not fluid build up), then it would lead to gains after some time. So pick optimal pressure to see expansion without injury.
I’m pretty sure duration you can do depends on how long you pump. After few months of pumping people usually get used to that and adapt. After year or few of pumping people can do even 40-60 minutes session. So you probably can either aim at gains, or getting used for pumping (outer tissue has to adapt to that).
Starting : 7.6 BPEL, 5.5 MEG
Current: 8.1 BPEL, 5.7 MEG
Goal: To understand what makes penis to grow.