What is the relationship with regards to hormone levels if one can achieve erections during the night but not during the day
It may be due to several different factors. Mainly e2/TT ratio
I have guys with total T of 190 and can pop boners any time of the day or night better then guys on 1000 TT. People are playing too many number games. Do I agree that number is too low, Yes but they can function perfectly fine other wise, so low T in these cases are not libido issues but may lead to other issues with cardio vascular, diabetes and other issues associated with low T later on in life. I think its all depends upon genetics as every one set point is different. Some people set point are at 350-400 other are at 600-800. I am finding its really a crap shot and dealing with other issues outside hormones in younger guys helps resolves issues majority of times.
I am not a medical Dr, please keep in mind that this answer is for information purposes only, and is not intended to diagnose, treat or replace sound medical advice from your physician or health care provider.
Night time erections usually happen during REM and have nothing to do with sex. Towards morning, a lot of times you have to urinate and that will cause an erection. Day time erections are purely psychological, unless you get direct stimulation. Totally different from night time erections. I agree with Matrix on this one, that low test doesn't mean you can't get it up. Now if you took Deca, I'd say that's what you get!
daytime and night time erections are all good!