Doing a bit of digging into galactic densities and the size of a star system, weeks would be theoretically possible, but it requires the conjunction of 3 star systems (Hoth, Anoat, and Bespin) to be unusually close for even the densest galaxy (and the starfield used portrayes a density close to our galaxy. The longer it takes to travel the more likely such a conjunction is. This is fiction so that isn’t particular important, but…

And its not like Vader was just sitting around waiting. He took off and then met up with Boba Fett on Bespin before the Falcon arrived. That also indicates some time has passed. But I think Luke’s training is the key point. The longer it lasts, the better Luke can be and the more complete the training. Because whatever Yoda didn’t cover in TESB, Luke no longer needed in ROTJ. That indicates the training was pretty complete.