Bucket size is the size of the chunk that DAZ|studio asks the 3delight renderer to produce at each step - making it smaller can help when memory is running tight, but progress may at least seem slower (not sure if the extra packets back-and-forth actually affect the speed). Raytrace depth is how many times a ray of light is allowed to bounce from a reflective surface or pass through a refractive surface to another before the renderer calls it quits and just takes the current value: the higher you make it the longer the render will take, so turn it up only if you are going to be able to see the effect of the extra steps.