A few minutes ago, we made the Rise of Azshara PTR available for download and install. This is so that initial testers will be completely ready to log in when the test realms are made public.
We are not at that point yet, and we don’t know how long it’s going to take to complete our checks and configuration. It looks like at least a few hours.
We’ll post here confirming when the PTR is playable and the PTR discussion subforums are open.