Actually, there is an explanation for this: http://starwars.wikia.com/wiki/Kessel_Run It's not about the time it took but rather the distance that was a result of superior navigation.
Hyperdrives work by creating shortcuts through hyperspace. A fast hyperdrive, like the one on the Milennium Falcon, creates a better shortcut and allows the ship to move through less space between points A and B.
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