The exact 'physics' behind hyperspace has been an ever-evolving thing in my RP campaign. In the first movies, we are shown hyperspace jump times that seem incredibly short. For example, the trip from Tatooine to Alderaan doesn't seem to take more than an hour or so—even though Tatooine is on the outer-rim and Alderaan is a 'core' world. Likewise, we see that the Death Star makes it from Alderaan to Yavin within a single day.
In the RPG (notably in the various sourcebooks), they largely ignore these transit times, possibly writing them off as simply cinematic devices. Instead, we're giving slightly more 'realistic' jump times of hours and even days. This is the rule I used throughout most of my campaign. With journeys from the rim to the core taking quite some time.
When the prequels came out, the amazing speed of hyperspace travel was again on display. In just about every movie, we see folks travelling from Coruscant to the farthest reaches of the galaxy in what seems like only hours. Since this is shown time and again, we can't just write it off as a cinematic device, and I wouldn't want to just ignore it, since a lot of the major plot points in the movies depend on the timely arrival of forces from far distant locations.
So, what's the answer? Go with the seemingly incredible speeds shown in the movie? (meaning you could cross the galaxy in mere hours) or go with the realistic speeds of the game? (meaning it would take months to cross the galaxy). The answer is in between. And like a lot of things, the original 1987 rules described it best:
Question: How long does it take to get from planet A to star system B?
Answer: As long as you (the GM) want it to take.
It's obvious that George Lucas has made travel in the Star Wars galaxy travel 'at the speed of plot'. So that's what I've finally decided to run with in my own campaigns. And I've even developed my own technobabble theory/explanation for how it is possible. On the maps that have been appearing of the Star Wars galaxy, they have numerous major hyperspace trade routes. The original rules state that travel along well-charted lanes means that ships can move through hyperspace at much greater rates. Thus, utilizing these lane, you could cross vast distances of space almost instantly (in a few minutes). Then you'd have to 'exit' and set course for your final destination-going a bit slower to get there. Essentially, in my game, they work just like an interstate system.
Well, it works for me, anyway. Plus I would NOT want to try and bog myself or my game down with figuring out 'realistic' space travel times.