How long is it usually between this point and when the book is available for general download?
Based on the past 1st & 2nd Doc books, 1 to 2 weeks. It's worth the wait though as the errata that is reported here will be corrected and the general release pdf you'll see will be in better shape than the advance copy.
"There are some corners of the universe which have bred the most terrible things. Things which act against everything we believe in. They must be fought." - Second Doctor