OP. I would answer your question this way. A part of our mind was “broken” and we had to do methods to help us during the broken brain phase until we were “healed”. Now that we are healed / cured from stuttering, we need to teach our brain that we do not have to do methods that we used to prevent us from stuttering, this is what the experts refer to as muscle memory. Now we need to tech our muscle memory that we do not need to do those methods anymore. Will it take time yes. But the length of time will be different for each stutterer.