I don't think there's a peer review study, but in the quantified self community, it is common knowledge that you should take it early (5am - 10am) or you will h

I don't think there's a peer review study, but in the quantified self community, it is common knowledge that you should take it early (5am - 10am) or you will harm your sleep instead of helping it. It is a http://en.wikipedia.org/wiki/Zeitgeber http://en.wikipedia.org/wiki/Zeitgeber , and you might want to read http://www.gwern.net/Zeo http://www.gwern.net/Zeo