One hour. The liver can break down most of a standard smallish drink in an hour. But, the big BUT, some of it stays in the blood for a lot longer as described below.
A standard drink (a unit of alcohol) is defined as:
However. The amount of time any alcohol can be detected in your system depends on the type of test, as shown in the following table.
Time in body system
Blood 6 Hours
Breath 12-24 Hours (Breathalyzer)
Urine 12-24 Hours; 72 hours or more for newer test methods
Saliva 12-24 Hours
Hair 90 Days
People will generally experience the effects of a drink within 15 to 45 minutes. Yes, it is quite rapidly absorbed.
Alcohol is then broken down predominantly in the liver through the actions of an enzyme called alcohol dehydrogenase.