I used this build before, but stopped on about the 2nd day lol. If you wanna make the run faster after you take the quest go to the left stair case, and wait till you can pull the left and center group at once and kill'em, saves about 1-3m of time.
then recharge and atack the other two gropus when they get close .D
thats exactly what i do, the timing is nice I also found that to shave time off your run, you can immediately start charging toward smite area...you should make it through the choke before the grasping/nightmare patrol is there(although they will be close)
If you aggroed the 2 cows on the way out, just run back and forth a few seconds till shadowform is ready...The only reason I dont wait in the choke is because its too easy to get stuck in there since the 2 cows ALWAYS run in there and block you with high chances of rubberbanding.