They do have some durability issues. For example, Line uses incredibly thick bases, as well as massive edges to lessen rail and any other damage. Surface uses thinner bases and the average width edge to keep their skis light, which they successfully do. Line also uses Maple block cores, where Surface (I am pretty sure) uses a single piece of ash. Line's cores are known to be some of the strongest in the industry, but Lines are also much heavier than Surfaces.
The double time is one of Surface's least durability-challenged models. I have never heard of any Double Times breaking (except for the ones my friend broke, but he has an uncanny ability to break skis). Surface's main problem was with the 9 Life, and then the first No Times snapping pretty easily. This year, they redesigned the No Time core to make it stronger.
But Double Times are not skis you should worry too much about breaking. They are real strong, beefy skis, due to their thickness and stiffness.
And I officially sound like I should work for Surface. Anyone want to put in a good word with them for me?