I think the official explanation is that he really said 'para-secs' -- presumably a space term for a very tiny fraction of time. I still prefer the explanatin that Han was just bullshitting badly. Optionally, maybe the 'Kessel Run' isn't a race over a certain distance, but, for instance, a measure of how far you can fly at top speed before the hyperdrive fails -- that would make sense for the Falcon!