I'm reading Dr Sarah Myhill's treatment plan in which she writes that it's ideal to sleep for nine hours, if possible between 9:30pm and 6:30am (during hours of darkness, a bit less for summer, bit more for winter). She says that an hour of sleep before midnight is worth two after because human growth hormone is produced during the hours of sleep before midnight. Is this true? I normally sleep between midnight and 7am (sometimes later) and am wondering whether to heroically try to shift my sleep pattern forward two and a half hours! It will take some doing but if I am going to wake up in a better state it will be worth it. Is there some good empirical evidence behind this?