Silvercast earned the achievement
on June 6th, 2011 at 1:00 am
That was earned during the Cataclysm expansion.
* Shen'dralar reputation was removed as a requirement in patch 4.0.3 (Nov 3010).
Progress is pulled in real-time from the battle.net API. The value shown here is either the current reputation or the one recorded by the achievement - whichever is highest.