Most PBS stations air the NewsHour at 6pm. As for WITF and the 7pm airing of SS, I'm really surprised it's lasted this long. I believe it started on 1/13/1992, when Lamb Chop's Play-Along premiered. Though I noticed that now I think the 7pm airing is the previous day's episode, and it used to be the day's episode. I was told that it was put on at that time so that parents could enjoy watching Sesame Street with their children after they got home from work, back when the show did more to entertain parents than it does now. I don't even think parents watch TV with their kids anymore.