Our bodies can tolerate alcohol better in the early evening. A pint at lunchtime will make you feel drunk faster than the same pint taken later in the day.
In 1941 the first link to alcohol was reported in the scientific literature, this paper showed that alcohol was removed slower from the body during sleep. 
Then in 1956 results showed that the metabolism of alcohol, how it is broken down, was affected by the body clock . 5 lucky test subjects drank whiskey hourly for 2 days whilst the amount of alcohol in their blood and saliva was tested. There was a clear change in how fast their bodies were breaking down the alcohol so it could be removed from the body.
Many further experiments were carried out in the 1960's to 80's confirming these results, one can only imagine they had plenty of undergraduate students signing up as trial subjects.
Alcohol drunk in the morning is metabolised by your liver faster, and reaches your blood earlier, making you feel drunk faster, than if you had the same amount to drink in the early evening .
Blood alcohol levels are higher when drinking during the day. Adapted from Yap, 1993.
So how does the liver change its way that it breaks down alcohol? We think this is due to changing the concentration of an enzyme that metabolises alcohol, alcohol dehydrogenase. Experiments in rodents show that this enzyme is affected by the body clock . It seems that our bodies have evolved to produce less of this enzyme later in the day, so we are able to tolerate alcohol better later in the day.
So bear in mind the next time you have a pint down the pub at lunchtime, you'll probably only need a half.
 T. Danel and Y. Touitou, "Chronobiology of Alcohol : From Chronokinetics to Alcohol-related Alterations of the Circadian System," Chronobiology International, vol. 21, 2004, pp. 923-935.
 R.H.L. Wilson, E.J. Newman, and H.W. Newman, "Diurnal variation in rate of alcohol metabolism," Journal of Applied Physiology, vol. 8, 1956, p. 556.
 M. Yap, D.J. Mascord, G. a Starmer, and J.B. Whitfield, "Studies on the chronopharmacology of ethanol.," Alcohol and alcoholism, vol. 28, Jan. 1993, pp. 17-24.
 F. Salsano, I.P. Maly, and D. Sasse, "The circadian rhythm of intra-acinar profiles of alcohol dehydrogenase activity in rat liver: a microquantitative study," The Histochemical Journal, vol. 22, Aug. 1990, pp. 395-400.