We do it in our hospital under medical supervision when is very hard levels or at Domus Retreat our center when in some cases. There are a number of ways to do it. Cold turkey ( that I do not suggest) , medically supervised, titrating or inpatients rehab.
In most case the withdrawal symptoms last anywhere from 3 to 5 days. If you can have medical assistance at least by phone in case you need it is always better.
I just read your other post so am not sure what you are asking this for?