Not trying to be evasive or smart-a##, but you just never know until you see it on the charts. A minor fed member speaks frequently, and usually there is not much reaction, but watch for Bernanke. Other news is apparently leaked and the reaction begins early, but then sometimes if the news is very late the real moves may not start until London open. (Refering to US times.). Just my opinion from observing some charts and looking back at the calendar.
For scheduled speeches there will always be press there live. Media companies pay a lot to have someone listen in on the speech and immediately inform their company when something significant is said. For example, when Greenspan was head of the Fed, he started one speech with the word, "unfortunately" and the Dollar tumbled within seconds.
