In Empire Strikes Back, how long are Han, Leia, C3P0, Chewie and R2D2 hiding in the asteroid from the Empire?

It doesn't seem like it's more than a day or even a few days. And if that's the case, how can Yoda teach Luke so much about being Jedi in a few days what it takes other Jedi years to learn (remember Yoda says he doesn't like to start training Jedi who are so old). And even though Yoda says that Luke's training isn't finished, in Return of the Jedi, he says there's nothing else to learn and the final test is to fight Darth Vader.