You're doing something wonderful for your son.
I don't know much about physical withdrawal from spice. But in terms of emotional withdrawal, I would say 30 days is too short. I quit drinking for 30 days earlier this year, and all it did was make me go back with a vengeance. It was long enough to make me very uncomfortable, but not long enough to force me to start handling my life differently. Right around the point where I should have started developing new habits, it was so close to the end of the month that I just waited it out.
This time I bargained with myself that I would try it for 90. I'm a bit over two months now and, having this time integrated new healthy routines to help me deal with stress substance-free, I now really value and appreciate my clear head.
Good luck to you and to your son. He's lucky to have you.