Timing an event to have maximum effect on a presidential election

Suppose that you were someone with a lot of power to sway a presidential election outcome - maybe you’re a movie producer releasing a movie that will change the views of millions of voters, or you’re a foreign government with the power to influence a U.S. presidential election outcome (for instance, China suddenly doing something militarily/politically drastic), or a whistleblower with knowledge of a political scandal (i.e., bribery, murder, etc.) that could bring down a candidate.
What would be the best timing for you to do so?
3 weeks before the election?

1 week before the election?

3 days before the election?

Obviously you have weeks of sensationalist advertising leading up to a fantastic event followed by additional events leading into the election.

When was Citizens United planning on releasing that video slandering Clinton?

Perhaps you’ve heard the term “October Surprise” to describe exactly what you’re talking about. According to the cite, the prime dates have been:

1968 – October 30
1972 – October 26
1980 – at least a month before the election
1992 – October 30
2000 – November 3
2004 – October 27, 29
2008 – October 31
2012 – September 17

Except for a couple of outliers, it would seem the prefered time for a sensation is the last week before the election.