Q: How long does it take to an average person to sober up completely after being drunk? Let's suppose person A gets very drunk at 11 PM on a Monday. By what hour on what day might we expect person A to finally become 100% sober?
A: The average person can metabolize about 1 standard drink per hour, which is a) a mixed drink containing 1.25 oz. of 80 proof liquor, b) a 12-oz. American pilsner beer containing about 5% alcohol by volume, c) a 5 oz. glass of wine, or d) one 1.25 oz. shot of 80 proof liquor. To approximate how long it would take to sober up after drinking alcohol, you'd need to count the number of standard drinks you've consumed (adjusting for larger/stronger drinks) and wait that many hours. There's no way to speed up the process (e.g., drinking coffee, taking a cold shower, eating, etc.) -- once you've ingested the alcohol, you just have to wait for your body to metabolize it.
Using the example above and assuming an average person weighs 150 lbs, they will reach a blood alcohol content of roughly 0.16% after about 7 standard drinks. This is twice the legal limit to drive, which is a reasonable definition of "very drunk." To sober up would therefore take 7 hours. Tolerance (i.e., experience drinking) doesn't affect this at all, and again nothing can shorten the time it takes to metabolize the alcohol.