When Adam first visits Saturn he is gone for 2 hours but it only feels like a couple seconds. At the end of the movie Beetlejuice sends Barbara there and she's back riding a sandworm in 10 seconds flat. What am I missing here?
shareBabs is a snake-charmer.
shareThe desert represents the sands of time and the way I see it is that time and space changes the more experience they gain just like they have more powers. Adam and Barbara go to the afterlife for a few minutes, they return, and it's three months later. They go there again, come back and Lydia's still there talking to Beetlejuice.
The spirits also seem to gain experience from Beetlejuice himself. Example, Beetlejuice posseses Barbara in the model, when they get out of the model she tells Adam she has an idea and they then possess the Deetzes and their guests.
As for how she got on the sandworm, she obviously just hovered through the air, again through being more powerful than when she was last out in the desert. Just like Beetlejuice hovered through the air when he came out of his coffin, and she and Adam made Lydia hover at the end.