From a recent "Journal of Neuroscience" article researchers found cannabinoids impaired the bodies circadian rhythms in mice. Very similar mechanism occur in humans so the effect is likely to exist as well.
From my previous years of personal research "cough, cough" I'd have to concur. I still think it is 1994 or there abouts.
http://www.jneurosci.org/cgi/content...ct/30/30/10061