Testing during the absorptive phase. This is a corollary of the rise in alcohol defense. Alcohol cannot affect or impair a person until it reaches the central nervous system, the brain. Alcohol cannot begin the process of reaching the brain until it is absorbed into the bloodstream. The blood, breath, or urine test will be unreliable if done while you are still actively absorbing alcohol and that usually takes anywhere from 45 minutes to three hours to complete absorption. And this can be delayed if food is present in the stomach. Thus alcohol consumed within 45 minutes before driving might be reflected in a blood alcohol content test performed an hour or so after driving is concluded. But those last drinks could not have affected your driving ability because they were not absorbed at the time of driving.