b) communicating something. If it's this, then I strongly suspect that McGonagall is cooperating with future Harry in some rescue plan. She might be communicating a simple message like "Don't worry" or "We'll get you out" which would imply that she has some extra knowledge about how things are going to play out.
But what she told Hermione shouldn't be very important as there was no way to know that Hermione, in her tired state, would understand the significance of whatever McGonagall mouthed.
Dumbledore says "if it is not dismissed soon, some of us may miss their entire luncheon". That means the hearing is taking place in the morning. The earliest future!Harry can show up is 3pm.
Of course, she could have information from future!Dumbledore or Harry could have sent a note via Margaret Bulstrode.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight, nine, ten.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: