Delayed sleep phase (DSPS)

This isn’t ‘bad sleep hygiene’ — it’s physiology. In a substantial subgroup with ADHD the circadian rhythm is delayed: the internal-clock marker (DLMO, the start of melatonin release) appears later than in neurotypical people — roughly 45 minutes in children and about 90 minutes in adults (a subgroup, not everyone). In autism the evidence is more mixed: prepubertal autistic children tend to show a later melatonin onset, but findings in autistic adults are inconsistent. The brain simply doesn’t get the ‘time to sleep’ signal at a normal hour. That’s why interventions that shift the clock (morning light, melatonin at the right time) beat ‘just lie down earlier’.