Overnight erections from the arousal peptide usually aren't dangerous the way true ischemic priapism would be. The real risk comes from combining it with certain other medications, things like trazodone or antipsychotics.
Saw someone describe a similar situation elsewhere, mid-40s guy with zero prior sexual function issues who just wanted to see what this peptide would actually feel like. Dosed roughly 1.75mg through an intracavernosal injection one evening, about three hours before bed and an hour after eating dinner. Reported feeling nothing whatsoever, spent a few hours listening to music, then just fell asleep normally.
Given all that, won't personally push past 1mg of that peptide within any single 24 hour stretch going forward.
How many hours symptoms last can help point toward a diagnosis, but it's probably less important than whatever other symptoms show up alongside it. There's decent background reading out there on trazodone-induced priapism specifically if anyone wants more context on the mechanism involved.