I also agree with the physical activity/screen time cut-off. I regret it every time when I fail on this.
Also for our DS8, we do NOT do a bath just before bedtime. It is not only not soothing - it absolutely winds him up what with all the sensations and water experiments and interesting trains of thought you can have when you are totally underwater except for your nose. Bath must be before dinner on bath nights or else we just skip it. Don't know if this would apply to your child.
Also - we saw a dramatic improvement in willingness to go to bed on his own when we got a dog that sleeps with him every night. In fact the dog helped in about a thousand different ways....
Occasional melatonin helps when we've GOT to get him to sleep and routine is all messed up. But I have to give it to him early in the evening or there's no getting him up in the morning.
To answer your question more directly - I can't see that any cut-off of necessary scaffolding would be the right answer, partly for a kid we all know is highly asynchronous. Lack of sleep only makes everything worse. If the scaffolding starts to feel wrong to you and/or your child, probably the right answer is re-investigating why it's needed. I say "re-investigating" because I have no doubt you're constantly working on this and all the other myriad stuff your kiddo needs!
