How does this interact with time zones?

I travel back and forth between Singapore, for reasonable lengths at a time, and to ease the jet lag adjustment period I choose to be a morning person in one and a night owl in the other. It works pretty well.

Is the hypothesis that your body naturally gets tired some number of hours after the sun goes down?

To all the people commenting about how this article "hits home": what is jetlag like for you? If you travel 5 time zones away do you become a morning person? Have you tried to keep that, but does it slip away and you revert to staying up late?