I always find the sooner the divider is up the better for both parties. On my first ever CW flight I remember the lady put the divider up straight away and I was a bit put out, now I don't think anything of it. She also wanted it lowered for landing so she could look out the window (landing in Barbados), I put it straight back up however when she lowered it in a kind of defiance for her putting it up in the first place, again, now I would not care either way if they wanted to look out the window.