I think it should probably be PUT or PATCH. POST is usually used to create a resource; PUT/PATCH is used to update, even if that update has an expiration (i.e. the horn stops honking.)
Exactly. That means this request is not idempotent, so PUT shouldn't be used. Of GET, PUT, POST and DELETE, only POST is not supposed to be idempotent, so it would be the preferred method to use for this request.