Wrocas let us know that the PTR servers are currently getting another patch applied to them. They will be down for maintenance between four and six hours today. This means that they should be up around 6 p.m. or 7 p.m. EST.
Hopefully this new PTR patch will bring about the reopening on the Sunwell Plateau, which was recently closed due to some large (and still undefined) bug. Other things that might be coming with this new PTR patch include more access to Season 4 gear, new changes and updates to class tweaks, and some spell haste changes.
WoW Insider will have the latest for you on patch 2.4 and the PTR. Stay tuned!