Thanks for everyone's advice.

Session 2:

I used a timer to keep it to 1 minute which was pretty short. I now think I was on 2 - 3 mins last night for my first session. Woops.

I did my normal stretch routine just before going on. Once on, I found that I'm still tight in the abs and neck (no surprise), but not as much as last night. I felt some stretch in my top right thigh and also my lower center back, close to the hips.

I was at 45 degrees. I let the arms hang, but they go down further because they are outside the backing board. It's a little like the stretch we do when we arch over an inflatable ball, foam roller or yoga bolster. But more extreme. I can still feel it in my left chest.

No dark red hands and purple finger tips this time.

I think I'm okay with 45 degrees and a true cap of 1 minute. I'll do it again tonight and then based on feel, I will increase the time at some point.

I still debate on letting the arms go or holding them up.