An average borderline amount above which the risk of a hangover increases is about three to five drinks over a two-hour time span. Keep in mind, however, that body size and composition determine how much an individual can drink in a given period of time. A small, slight person simply can't down drink for drink with a large, muscular person. A reasonable average pace is one drink per hour, with one glass of water for each drink to dilute the alcohol and minimize dehydration. And mix your drinks with water rather than with a carbonated beverage.
Carbonation speeds the absorption of alcohol into the blood stream.
As a general rule of thumb, it takes as many hours to sober up as the number of drinks consumed. The liver needs the time to metabolize the alcohol. There is no way to sober up quickly. Coffee, the traditional sobering-up brew, offers little help. Actually, it can make things worse by disrupting sleep.