My body is like an alarm clock. I also don't sleep well, never have and barely get any sleep during the night away. I am up at 5 am regardless of what I am doing. I hate it.
The only time I sleep about half an hour/hour later is if we went to a party (wedding, etc.) the night before or when we are on vacation - I might get an extra 30 minutes or so.
Because of this - I fall asleep very early in the eve.