if the person is under the influence now. they will keep them there until they are sober and most likely send them home once they sober up. It takes 1 hour for the blood alcohol level to drop .20 points - I think if I remember this correctly.
If you are looking to get someone sobered up that is all they basically do, but if they are suicidal or are in pain and hurting they will keep them -
Please keep us posted as to what is going on.