Coaches get judged on results - leave it too long to change things and you're out of a job. Or you get stuck in a halfway house which becomes the norm. From previous leadership roles, my experience is you set your standard from the start. Going slowly just leads to mixed messages and a confused/directionless team.
Like I said, the irony is that the agitators were moved on by Ivan.
This. I am not an Ivan fan, purely based on his results, but he has done the right thing by making the changes quickly and making it clear what is expected. Cultural change doesn't happen overnight, but it certainly doesn't happen if you don't make it clear from day one what is expected of the team.
In my experience, it becomes immediately clear this who will embrace the change and those who will never change. Time does not move those people, they just cause unrest and disaffection amongst the group because typically, they whinge and complain and try and turn the others against the new leader.