Whats the 12 hour rule for

respect for their own host site.

Basic respect for their wishes but most of all :
-The people who actually make an effort to search for it, go on their website (and thank them while at it) can enjoy it first
-It allows them in case of mistake (typo, missing page, wrong translation...) to take down the chapter, correct it and repost a better version before it's spread everywhere.

Thanks