There are a few reasons today could be a big day
The FBI tradition is to not make any politically-sensitive moves 60 days before an election.
The US mid-terms are on November 7 and that makes next Friday the unofficial deadline. However, that would be cutting it awfully close and making the move ahead of Labor Day might be less-problematic.
On top of that, Mueller’s prior indictments have mostly come on Fridays.
Roger Stone believes he’s facing an imminent indictment and yesterday released a letter pleading for help with a legal defense fund. He said Mueller is “examining every aspect of my personal, private, family, social, business and political life.” In part because of hints he made that he had foreknowledge of hacks and releases of Podesta emails.
Others dispute that the 60-day guideline, which is an informal policy, even applies to someone like Roger Stone who isn’t a politician or formally working for any politician.
As for markets, I don’t think they would care about Roger Stone. Now if Don Jr. is indicted on the other hand…