WW's now have inherent armor. It varies depending on level. From the uesp wiki:
The armor rating is 0 at level 1 and then increasing in 50 point intervals every fifth level, beginning at level 11. The maximum rating is 400 at level 46.
Also, I don't see the 4 minutes for Dragonhide. It is inherently 30 seconds. With stability that can increase to 45. With a 100% fortify potion you are up to 90 seconds. There is no way to dual cast Dragonhide, it is a master level spell so you are already using two hands.
Good info on the Werewolf. Thank you. I thought I liked werewolf when I tried it out a few weeks ago. Much stronger than I remember before Dawnguard.
Ah, Dragonhide is the one of the few Master level spells that can be dual cast. The animation is the same, but it uses the usual 2.6x magicka for 2.2x power. It was an exciting discovery for me as well, when someone else here mentioned it some months ago. With Stability and Dual Cast 45 second Dragonhide becomes 99 second Dragonhide. With 100% Fortify Alteration, it becomes 198 seconds. I think you can get fortify alteration to 120% without enchanting anything yourself. And you can get it up to 160% if you do the maxing out alchemy enchanting thing.
I think there are perhaps several other master spells that benefit from dual casting. Perhaps that restoration master spell, or maybe the illusion spells. But I haven't tried those yet.