Depends. Are you asking about the canon Kessel run, or the objectively superior EU version?
In the EU pre-Disney, Kessel was a black hole and there was a race around it. The more powerful your engines, the closer you could get to the black hole. Which is why Han used a distance measurement instead of time (of course, the most likely in-universe fan theory is that Han was BSing the two farm yokels by throwing out space technobabble, but Star Wars authors never settle for the easy answer when they could write an entire book to fill in the plot-hole).