>=9h of sleep is imho too much. Regarding sleep there is much contradicting research and books [0], but most stuff I read (not citing anything) points to 7-8h as a sweet spot and some doctors say that some people need less sleep for reasons (tm). Anyway back to my point: A graph on teen sleep showing 9 or more hours in percent is a bad proof of worse sleep schedules in teens since imho more than 9 hours of sleep could be bad for you as well...