Poser DOF is incredibly slow. Fortunately, you can render a depth map (in P9/PP2012 at least), and then either use a Photoshop plugin like DOF Pro (which is easy), or use the depth map as an alpha channel and do some Photoshop magic (which is confusing, and which I have to look up how to do everytime I use it, which is why I bought DOF Pro). If you do DOF in post, you don't want to use post filtering. (If you use it, the depth map either isn't filtered, or is filtered differently, and you get nasty halo effects.) You can alway do post filtering either in postwork, or by taking your render and using it as a self-illuminating background in a subsequent render.