Just a random thought:
MOP
Announced on 25th July (Thursday)
Released on 23th Sept (Tuesday 8 weeks 5 days later)
5.0 PTR released 20th July (Saturday 5 days before announcement)
WOD
Announced on 14th August (Thursday)
Released on 14 Oct (Tueday 8 weeks 5 days later) ????
6.0 PTR released 9th August (Saturday 5 days before announcement) ????
Things we already know:
6.0 PTR will last 1 month ~
The content for the 6.0 PTR is already ready with the last beta build.