Check out this interesting article which discusses the impact of daylight-saving time on your body's internal clock.
Also this
article on 'clock genes' and circadian rhythms by the
University of Utah's
Genetic Science Learning Center. And this one which talks about how "we can't touch time, or smell it. Yet it is utterly inescapable. But, research shows, time is - at least partly - something we control in our head".