You have asked a very good question.
And I think that six months is a bit excessive, but it is clear that before opening the belt there must be a period in which the girls still wear the belt and the causes are openly discussed, the causes can be several , disappointment with the situation, with the keyholder, variation in the situation...
As much as possible, the keyholder should "try to seduce her" making her feel comfortable again, as a keyholder I also enjoy my responsibility, and if it is not capable, it is evident that the belt must disappear.
I also recognize that it would not be the same with the girls as with @Yolanda a, with them I have more room to negotiate and, furthermore, in the event that my wife asked to leave It and the girls continued, the truth is that moral problems would arise.
An advantage of the girls not being alone is that they encourage each other, give each other advice and a little peer pressure also works.