He's right. There is only so much that one can gain from being in inpatient care for so long. I went to inpatient for 30 days and the same stuff is regurgitated over and over again with the same guest speakers. Half that time would have been more than enough. It can be easy to see how someone would want out early. At this point, he probably won't gain anymore knowledge or help from inpatient treatment.
When he does get out, try not to be highly overbearing. That may be a lot to ask, but he will need his space to get things done without people trying to be so vigilant of his actions. Certainly don't ask if he has been using/drinking. Time will tell.