Bottom line here though, is this whole question is nonsense. It's not going to happen. Hillary will not step down for any reason. Even if they dragged her away in handcuffs she would not step down. Nor do I believe that Comey would move to arrest her until after the election if that were the case. So mostly my comments were more in jest than a real answer. Instead I was offering up my belief of what the weak kneed Republicans would do, that being to bend over for the Democrats.
The date of the Federal election is set by law. Congress would have to convene and change the law, and it still cannot be later than the first Wednesday of December, when the Constitution requires the electors for the Electoral College to meet.