6 hours for me and it dropped. Saw some people join the 30+ mage group and get in in 5 minutes, others as long as me.
It is tradeable if you are in a large group, have seen 2 drop for 1 person in 2 consecutive mobs.
I got mine in about an hour of farming moon guards with 4 other mages in party
I joined a raid group that farmed Moonguard Stronghold. The size varied between 6 and 10 people. One mage got it in 5 minutes of joining. I was also lucky, The Stars' Design dropped for me after 25 minutes.