Been running Sethekk since patch, got my reins yesterday, takes about 15-20 mins, even if i accidently pull a pack. I'm PVE Disc.
Generally I mind soothe anything that i can skip, and take down the pairs of guards using smite/atonement. PWB and PS on ravenguards, Holy nova on the packs of non elite birds. Anzu himself is cake, just prehot and shield for the silences, and use archangel to get the mana back after the mana drain thing he does.
Good luck fellow priests!