Ming from Agents of Speech explains that stimming in autistic people is often automatic and hard to stop once it starts. Stimming beyond five minutes can make self-regulation difficult. He recommends allowing it at home, using behavioral systems to limit it in public, and explaining the reasons so the person understands.
When I talk to some more mature autistic children or people, the stimming just happens. They didn't plan it, they didn't want it. It just came, and they automatically did it. As some of the autistic adults tell me, stimming is like a rabbit hole. A rabbit hole that, you know, it's okay to go in for a bit in the appropriate times when no one's around, when it's okay, socially speaking. But anything over five minutes is actually quite dangerous because they cannot bring themselves out. They cannot really regulate behavior themselves. And you have to give them systems to do so. So what you can do is that you can allow them to do it inside of the house and use behavior systems to tell them not to do it outside. And you need to tell them the reasons as well. So it helps them to understand the reason behind. And this is for more mature people.
