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We really don't know how long passes:

1. Between Luke leaving Han at the cantina before they hook up again.

2. On the Millenium Falcon in space

3. On Yavin 4 after Luke arrives

I never got the impression that Star Wars takes place over the course of a single day. I realize that the SW universe isn't huge on the technical specifics, but I would think that the space travel would take a while:

Tatooine -> Alderaan (or what's left of it)
Death Star -> Yavin IV

That stuff has to take longer than a couple of hours. Doesn't it? Especially if Tatooine is so remote, as has been mentioned in both Episode IV and I.

But then there's Vader's line (paraphrasing) "This'll be a day long remembered. It has seen the end of Kenobi, and it'll soon see the end of the Rebellion." That certainly implies that at least the last half of SW happens in a single day.

I even think it's possible that Luke takes Ben to Mos Eisely a day AFTER he finds his uncle and aunt killed. There's no indication as to whether the trip is immediate, or if they go back to Ben's place for a night's sleep.

At least with Tatooine, it appears that two days went by. The first was when Artoo was travelling by himself through the canyons; it looked like late afternoon or early evening. Then there was the the scene where Luke longingly gazes at the twin sunsets.

I always had more problems figuring out the timeline with TESB. Since the Falcon's hyperdrive system was kaput, Han obviously needed much more time to travel around, let alone make a pitstop: "Bespin's pretty far, but I think we can make it." Travelling from planet to planet, system to system doesn't sound like a couple hours of flying.

And what about Luke's training? It appeared nothing more than a crash course, even though a Jedi's training needs a lot of time. I'm sure his rigorous regimen took course over a few days, maybe longer.

Another thing we don't know is just how long a day is on Tattoine. Are we to assume the planet takes 24 earth-hours to revolve?

I always had the impression that Empire took weeks/months. We get no clear indication but, as you say, plenty of clues. The hyperdrive was broken and Luke's training seems to have pretty much been completed by the end ("No more training do you require", Yoda says in RotJ).

I think it's a few months of travel and training, compressed on screen to a couple of hours.

There must be a site out there that explains this...

I've always thought all the movies took a few days, but its conceivable that from the time Luke wakes up til the time he blows up the Death Star it's only one day. What an awful day.

That's a Jack Bauer day, my friend!

Did these people ever go to the restroom? I wonder how Darth Vader took a shit.

"He's more machine now, than man. Twisted and constipated."

That's exactly what I was thinking...

Rebel officer: "Luke! You turned off your targetting computer! What's wrong?"

Luke (in raspy Bauer voice): "WE DON'T HAVE ENOUGH TIME!!!"

Jack Bauer has had worse.

EDIT: Dammit, I just noticed someone beat me to a Jack Bauer referrence.