How long does roll take to end?
I'm not sure about the visual frames for the duration of the roll, but there is no difference between "light/mid/heavy" roll in DkS2. The only thing that encumbrance affects is the distance of the roll in total.
You can find more information about the roll mechanic, including roll speeds, Agility, Adaptability, and Encumbrance affect on the roll mechanic on the wiki