Work Ethic
A dozen seconds was an inconsequential amount of time for most mortals. Unless one was performing some excruciatingly difficult task, such as performing a plank or counting down the timer on a microwaves for food when starving, it would pass without even giving enough time for significant thought. A good stretch early in the morning would easily surpass such a time limit, and there was certainly almost no task that required less time.
Yet for immortals, 12 seconds was an eternity. With minds fast and powerful enough to work through countless scenarios and resolve an untold number of issues, each second was enough to determine life and death. It was ironic, really, considering that the greater their cultivation level became, the longer their fights took.