Rapid Defense and You

I suppose it's the inner desire for mid-air battles that inspired Blizzard to create the timed daily achievements that require you to complete the mounted abilities within two minutes. I distinctly recall Bombs Away being very easy, though I have reservations about Blade's Edge Bomberman being a success without a speed boost, supposedly it is possible at 80 using the "double bomb trick".

However, due to its current popularity, Rapid Defense is challenging not only because of the distance you must cover and the mobs you must destroy, but competition from other players doing the daily.

The easiest solution to the later difficulty is to do the quest in the morning hours of the server; otherwise, you will have to deal with a considerate amount of other players. My personal frustration with this was recognizing that there were many dragons and drakes to the north of Wyrmrest, but everyone, including people not working on the achievement, always focuses on the mobs south of the Temple due to proximity to the Azure Dragonshire. Since these are the mobs you need in order to complete the quest on time, you need free reign over this section.

As a Hunter, I have the benefits of using both Aspect of the Cheetah (to run to the mount once the quest was accepted) and Track Dragonkin. The tracking was particularly useful to find pockets of three or four drakes and dragons. I highly recommend using some form of speed boost in the period between accepting the quest and getting on the mount to shave off some very needed seconds.

Once mounted, head south as soon as possible, find a pocket of dragons and drakes, and start attacking. Drakes only require one fireball (1) and one DoT (2) to kill them, so don't waste more time than necessary on them. The dragons require a DoT and around three fireballs to do them in. If you can, take advantage of any mob that has already had its health lowered by the friendly NPC dragons. Use your heal as soon as you start taking damage, particularly if you are dealing with three or more drakes/dragons, as you should.

I highly recommend waiting to use your speed boost AFTER you finish at the Azure Dragonshire. Along the way you should have completed around 4/5 and 2/3 of the necessary mobs, such that there will be one or two of each available to kill on the way back. Becareful though: Make sure a mob dies before considering it a success - I've ended the quest several times thinking I was completed only to find one of the mobs didn't die.

Track the achievement to keep an eye out on the time, and if you fail, abandon the quest and try again.

Good luck!