^I like to think that Bespin was relatively close to Hoth -- say a light-year away -- and it took them that long to travel there. Time dilation from travelling at near-light velocities would have kept them from experiencing too much time loss (perhaps only a week or two passed between leaving Hoth and arriving at Bespin from their point of view?), and enough time would have elapsed for Yoda to have taught Luke enough about the Force for him to get as good with it as he was shown to be when he confronted Vader.