I have noted over the last few weeks of intermittent use of Melatonin seems to have a strong effect on nighttime erections.
Most notably for me the dosage seem best at 1mg taken before bed with effects starting to occur at around 1.5 hours but lasting up to 4 or more hours. Possibly should take it earlier to see if effects are at a more useful time.
Currently my T levels are mid range but erections and especially night time erections are few and far between, melatonin in my case seems to be having a positive effect in addressing this issue, one that many on TRT experience.