In this regard, I'd go with wikipedia. There are plenty of doctors who are wrong in the world--they are only human.
Thus the (informal) "half life" of one cup of coffee could be 4 hours, but two cups could be 8 hours, and so on.
(To the extent I can track the estimates of "3.5 to 6" or "5.7" hours of caffeine half-life back to original sources, it looks like the studies were done in 1978 and 1980. Maybe modern caffeine consumption has moved to a level where linear rather than exponential elimination dominates?)
Damn. I was hoping to calculate the optimal hour for a caffeine "booster" after the initial morning fix.
Looks like about 5 hours:
So, on average, your sleep specialists have about 13-15 years of schooling. It's about the same ammount of time that it would take to become a Plastic surgeon, or Interventional Cardiologist, Cardiothoracic Surgeon of Invasive Radiologist.
It's not a light weight course of study. Certainly not 4 hours worth.
Dr. Walsh in particular is a professor at the nearby St. Louis University. If you do a search on Medline for Dr. Walsh you will see that he is active and published with studies on sleep disorders.
http://www.stlukes-stl.com/services/sleep_medicine/research_...
People can build up a tolerance to caffeine by saturating the receptors in the brain that are activated by caffeine. So, after month of daily ingestion, some people can drink 4-8 cups of coffee a day and not have any problems. In this case, it's especially true that your mileage may vary greatly.
I used to be a caffeine fiend. But, when I started having sleep problems, I had to completely quit caffeine, and it does help. I could drink 2-3 triple espresso's in an all-nighter and then sleep like a baby when I was in college. Now, I drink 1/2 a cup of coffee and I'm buzzed for hours, and I don't sleep well that night.