If you were not scheduled for duty the unit cannot require a blood test, Breathalyzer, or other alcohol measuring device until such time as you would have normally reported for duty. For example if you are off duty and an alert is called you cannot be tested until the time you would have normally reported for duty. The alert is called at 0200 but your normal report time is 0630 you cannot be tested until 0630 hours. For more information see the AR 600-85 extract below
Extract AR 600-85 Para 3-8
Alcohol screening and confirmation tests should only be performed during duty hours when the Soldiers selected for testing have prior knowledge that they should be on duty. For example, if a commander calls an unannounced alert and Soldiers report for duty at 0430 when they were originally scheduled to report at 0630, then the alcohol test cannot be administered until at least 0630. However, if the Soldiers were previously told that they had to report at 0430, then they may be tested for alcohol at 0430.