Ray-traced shadows and occlusion plus transparency maps tend to be slow. I've also noticed that 3Delight can get hung up on edges, sometimes, though I've never been able to work out exactly what the trigger is. But check, if it's stuck at 0%, that it isn't a problem with tdlmake optimising images - if you go back to the main window, instead of the render window, you can drag the status bar to one side and expand it to see where DS is at.