Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
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:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
Presumably Harry or Quirrell has already figured out that Harry will be expected to do this (in fact, this may be why Quirrell told Harry to leave one time-turn in reserve). Here's one plan they could have come up with:
Quirrell removes himself from the action by pretending to be more tired than he is. Harry uses his time-turner to go back to eight o'clock, signal Quirrell, and tell him the password. Quirrell comes into Hogwarts, uses Imperius or Confundus or some kind of false memory charm on Flitwick to make him say he heard the password at three o'clock. Just after nine, Harry and Flitwick come into McGonagall's office, Flitwick says he heard the password at three, and Harry is off the hook.
For a particularly evil flourish, Harry could have polyjuiced into Quirrell and Quirrell into Harry before returning to Mary's Place, and Quirrell can just Confundus Flitwick himself without worrying about sending any signals, while Harry rests at St. Mungo's.
No way. They must have checked Harry for polyjuice and Harry wouldn't have posed any problem for Snape in subduing.