[From the site]
Coupla notes here: First, this is hardly scientific. It's based on the LD_50 of caffeine which is the amount of caffeine it would take to kill 1/2 the people in a given group if they were administered this dosage.
It's not based on a period of time, it's based on a concept similar to blood alcohol content, the amount in your blood would diminish over time.
Probably more importantly, before you ever got this much caffeine in your system the sugar content would put you into an insulin coma. The sugar'd kill ya long before the caffeine did.