Perhaps the six hour limit was placed on time travel a long time ago, by wizards much more powerful than today's, who knew (perhaps first-hand) how nightmarishly screwy time travel could get. This sort of thing has precedent: the Interdict of Merlin prevents the most powerful magical knowledge from being passed on in writing. The reasoning is similar, too: some magic is just that dangerous.
I would not be surprised if the destruction of Atlantis involved Time Travel. Especially if we consider that this fic might be influenced by "Harry Potter and the Wastelands of Time."
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.