The Scarab Gong starts and finishes the quest  , part of The Scepter of the Shifting Sands quest chain to open the Gates of Ahn'Qiraj. This quest is available until 10 hours have passed after the first person on the server has rung the gong.
This is part of the conclusion to quest chain:
Patches and hotfixes
Patch 1.9.0 (03-Jan-2006): Added