Hello there this is a quick way my friends and me tested out. I'm lvl 88 getting about half a bar per pull which takes anywhere from 2:15-2:30 depending on your dps.
!.) Find a good group and make sure the dps is good
2.) Q up for the instance
3.) once in the instance have your tank pull all the mobs from the front of the instance to the room just before the first boss
4.) have 2 of your dps run into the first bosses room and pull all the mobs a mage and hunter works best for this because they can pull and run away fast enough without dieing
5.) bring all the mobs they pulled back into the room just before the first boss and AoE them down.
6.) once all the mobs are dead leave instance grp and re Q and run it again
7.) just rinse and repeat its easy and if your good you can get the run done in about 2mins or so.
Thanks just figured id add a little tip other than questing or instance Q grinding all the way to 90
P.S a druid healer works best for running and healing