I used to not know about this but of course everyone has an idea of how it is. So, according to an article, going to bed earlier and waking up early matches human circadian rhythm which means internal clock that follows day lights patterns. Hence, I would definitely think that following natural patterns would give us the most productivity so far. And then, it depends on when you want to wake up, if you want to wake up at 6am count backwards 7-8 hours (general human time for rest) which is 10-11pm. Voila.