The best way to approach this, for those who want to do this the quickest way, is to join a server (best if it is official) that is empty, and just start firing away. I managed to get this achievement in around 6-7 hours, which calculated earlier, with approx 1,500 arrows an hour (10,000*2~3 seconds per shot=5.5~8.3Hrs).
The reason I suggest an empty official server is because the shot count becomes interrupted and begins to lose count between how much is recorded as "shot" and that which was actually shot. Make sure to keep refreshing the achievements page every 5 minutes, to make sure the count is still going. If it has not, then the game has hit a bug and needs to restarted, or the server has hit some problem (for whatever reason), in which case just go to another official server. In an empty server I had a ratio of (Recorded:Actual) shots, I had near 1:1. Not perfect since sometimes the game just stopped recording the count. When someone joins, that number has always immediately dropped, from 1:5 till about to nearly 1:50
So in conclusion, an empty server is by far the most reliable way to get this achievement and the quickest.