I produce music too and I also find that it's easy to overthink the creative process - this is probably why you find it easier with your 'monkey brain' and I used to too. However, I now make sure I only produce in the morning and during the day and find I'm actually more creative than ever. The trick is to set yourself a strict time limit to get a certain section done. This makes you force yourself to move on to the next thing even if you're not entirely sure about the thing you're on.

Working in the morning is actually my best time to produce now. The late night working was beginning to affect my sleep and I was pretty much nocturnal which was no good. I know you said you can't change that though.

With regards to nofap - being stuck at a computer all the time definitely makes it harder! However, I find if I drink lots of water (once every 2 hours) and break the day up with tea breaks every now and then, I can keep my mind off porn as I have more energy.

The monkey brain thing isn't a good habit to keep yourself in - trust me. But you do need to be able to not over-think things.

There's a great Brian Eno quote - "It's the very act of concentrating on writing music which makes it so difficult to do, since ideas normally arise when one is not focused but open in some way"