I was on a red eye last week and the FA specifically asked everyone to lower their shades as 'this is an overnight flight and we are chasing the sun' so by closing them now, no one would get woken up when the sun came up. This was before we pushed back. I was in F and noticed most people put them down immediately. Not a very safe thing to do IMO and she should have waited until we were in the air to make that announcement.