I'm more interested in the dual casting effects of Stoneskin and Transmute. I want to know so I can decide when/if I want to get the perk. I have the mage armor perk so the Stoneskin spell is very handy and I like to make my own jewelry so Transmute is as well. My next perk is 2/2 in mana regen, after that I was considering the dual casting alteration perk.

Increased duration is the effect from DC Alteration.