Following a similar path to what Wrathoftheeasymode did.
PTR 2months before estimated release.
Events in the weeks after.
6 weeks after ptr Patch goes live.
Release roughly 2months following ptr launch.
In this case the PTR DOESNT have any of the cata specific content given they want it to be a surprise to the majority - well as much as it can be with mmochamp and various other sites out and about datamining everything.