How investigative journalism works

This is the way investigative reporting normally works.

The reporter spends days or weeks or months collecting information, each item of which should be (ask Dan Rather) verified by at least three sources.
When the reporter is satisfied the information is as complete as possible, his/her last step is to call the subject of the story. "This is what I've got," says the reporter. "It will be in tomorrow's paper (or tonight's telecast). I want to make sure my information is correct. Will you go through it with me?"

Typically, the subject of the story will not be very happy to be talking to this reporter. Even if the reporter is talking to Mitt, and tells him the income tax returns are free of illegality, Mitt, if he is smart (and most of them are), will ask for time to check the documents. The two will set a deadline, and Mitt will go into damage control. The docs may not be illegal, but some of the content (legal loopholes, offshore techniques, etc.) may not endear him to potential voters.

This also buys Mitt time to tell reporters something like he has paid 13 percent over the last decade, or something else to show he has decided to cooperate, which looks much better than the story breaking cold.

In the old pre-Internet days, the Mitt-reporter deadline would have been keyed to the old, and very slow, news cycle: midnight tonight for The Washington Post, 4 p.m. Eastern for CBS. Now, the news cycle is 60 seconds long. It's 1:25 p.m. in California, 4:25 Eastern, I wouldn't be surprised if something didn't pop by 5 Eastern. Or, depending on deals still being made, early tomorrow.