With current skill speeds I found that the latest you can begin a combo for Huton Extend is 8-7s, for some reason unlike dots if you apply when the timer ticks from 1-0 it doesn't re-apply (gotta be server lag atm).

So i tend to treat Huton like a dot on myself now, 14s left means i have time for a fang combo and an armor crush comfrotably, or a AE or DE combo and armor crush so long as the add wont die (fucking bismark) or a mechanic isn't incoming (please stop making yourself untargeted ravana).