It says as late as 11pm. Another one says some of the later time can be explained by other things like light exposure. This seems to indicate that a 10pm bed time could be attainabke with a wake up time of 6 or 6:30 providing adequate sleep. Some of the studies show that even on weekends without the waking constraint teens are getting 7-8 hours or less. It's also indicative of weak influence when we see the remote learning being called a disaster yet these articles are touting the benefits of the extra sleep associated with them - where is the mitigating impact then?
Also from the articles, “As I often phrase it, multilevel interventions are needed,”. Why not start with the less intrusive interventions? Not all kids require a later start time, and could even be hurt by it. A later start time would have hurt me, for example. We need to make sure we aren't hurting some people in an effort to help others.
Perhaps the strongest evidence is that adults are not affected by the hormone related shift and yet they too do not get the recommended sleep. This points to the idea that environment and habit could be factors.
So far I see no absolute evidence of societal net benefit, largely because the studies ignore n-order impacts and fail to fully explore alternative explanations and remedies.
Don't forget, a lot of this is psychology and is just towing the line. They don't even know why bi-phasic sleep disappeared. I would love to see the data for adolescent sleep times and duration for the past 150 years, but it appears the studies completely ignore this. For knowing so little, they certainly are pushing hard for a specific change (a change that some of the studies don't believe will fix the issues, such as achievement gap, hormone altering light exposures, etc).
https://news.ycombinator.com/item?id=30690965