Apparently, the timing of sporting events in Beijing, probably driven by needs of American TV audiences, did not take into consideration the best time of day for athletic performance. But who cares about athletes, or even about breaking Olympic and world records, when delivering Joe Schmoe to the Budweiser commercial is much, much more important for the success of Olumpic games?!
This article provides a nice summary of the issue and the current state of understanding of the way circadian clocks affect athletic performance:
Science Says Athletes Perform Better At Night