We just killed Muru/Entropius at ~12:40 AM server on 9/10/10, and the third gate, Archonisus, is locked. Meaning we cannot access Kil'jaeden for a chance at Thori'dal.
The Third Sunwell gate should be down now, Dryssa. You may need to perform a soft reset with your raid to see the effect, however.
Instance Soft Reset
-Disband your raid
-Have everyone in your raid exit the instance and remain out of the instance for no less than 30 minutes
-Reform and enter the raid again