A few hours ago the Zcash GitHUB Page was updated to reflect a later launch date.
The original date of September 5th 2016 has now been updated to September 26th 2016, I assume this slip in timing is due to the “Mock Testing” milestone which is currently overdue by about 1 month.
I have also updated this sites pages and countdown timer to reflect this change.
Src: https://github.com/zcash/zcash/milestones 
