It's the NHL site that leaves the brackets open until Sunday. It was the same last year too with it being open after the first games had been played. Personally, I don't think it matters all that much, unless someone has predicted a sweep, but I see the point.
I've got my bracket locked in and would ask everyone to do the same before the first games Saturday. I'll close entry to the bracket pool here once the first games start and ask everyone to refrain from editing their own bracket after the fact.
Well let's say a star, maybe a goalie gets injured Sat or Sun, it changes things.