Where is that written? I well remember that no chain of time turners can send information (at least information comprehensible by humans) back more than 6 hours, but that still allows one to add those 6 hours more than once a day, especially with multiple time turners.
Ch 17:
Harry:
"...Sorry to ask but I was wondering, is it possible to get more than six hours if you use more than one Time-Turner? Because it's pretty impressive if you're doing all that on just thirty hours a day."
Dumbledore:
"I'm afraid Time doesn't like being stretched out too much," said Dumbledore after the slight pause, "and yet we ourselves seem to be a little too large for it, and so it's a constant struggle to fit our lives into Time."
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 116.
There is 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.)