LSW is pretty episodic, with each "chapter" completable in around ten minutes. Of course, you _could_ spend considerably more time than that, and will probably want to, but it still doesn't have to suck up more than an hour or so per play session. And you already know the story, so you shouldn't have to spend too many cycles on "OMG, what happens next?!?"

The scene in _Empire_ where Lego-Vader shows Lego-Luke the Polaroid of Lego-Anakin and Lego-Padme is flipping hilarious, one of many such moments.