We waited a fair amount of time for darth, but it was pretty early in the day on one of the first days it was open. That said, if you are claustrophobic like I am, the hallway where the line is may be a problem for you. It was narrow and packed with people. There was an emergency/cast member door with a small alcove off one part of the hall, so I stood in that for a little bit. The high ceilings in most of it were the only thing that made me able to stay in the line. Hmm, maybe the narrow tunnel like part with a lower ceiling started my problem there...that was at the start of the line.
Also, the chewbacca meet is not a visa meet. It is beside a non-visa darth meet. The visa darth meet is kind of through where you see greedo and the jawas. You don't go downstairs for it, but you do for the two non-visa meets.