As much as I enjoyed the initial movie (and to some extent, the initial two sequels), they didn't live up to their promise of a vaguely credible science.
Remember, back in 1977 "Science Fiction" was mostly still synonymous with "we don't care about reality", some blinking lights on a cardboard box meant "sophisticated futuristic device" and people in space were wearing bronze deep-see diver helmets over leather jackets, jodhpurs and riding boots...
Star Wars™, first of his name, went the 2001 Space Odyssey™ path and featured what looked like a realistic, or at least believable futuristic world. Except this was just pretense, and the world's workings underneath were as realistic as those of Sesame Street™ (or similar hard science shows)...
TL;DR - Saying "Hurry up, it's 20 parsecs to 8" is just standard Star Wars™ grade science...