Suddenly
No Punting
It depends on the speed of this investigation. So far it's just "looking at emails". If there isn't anything further from the FBI until after the election then I doubt it will last longer than a news cycle and won't make much movement in the polls.
I think it will move the polls. We are talking voters on the fence, and most of these people are working more from emotion. They are balancing Trump being an awful person against the belief that Hillary is a corrupt liar. This will move the needle for those people.
The news cycle thing is the biggie. If the Hillary campaign or anyone else has any really nasty anti-Trump surprises in reserve, expect them to be rolled out tomorrow. Of course, there is a healthy chance Trump will be an idiot and hijack his own positive news cycle by saying or doing something really stupid.