Despite all the math, I generally avoid fracture in short fights. I'd say if a fight is 3 mins or less, you should really only be applying it under the effect of some kind of buff (berserk / unchained). Other than that, it doesn't boost your dps by a whole lot. Longer fights where there are no stops, and you have full uptime for a prolonged period of time, fracture will start to give gains overall.

Something else to keep in mind, is if a boss or monster becomes un-targetable, it is immune to all dmg, and that goes for dots as well, so don't waste a GCD on fracture if something is going to jump, it won't do you any good.