That seems a very, very strange case. I've never heard of anything like that before to be honest.
Either way, it very much depends. The last render I posted (first post on page 3) took about 8 minutes to render. That's Vray using some pretty high AA, full primary and secondary indirect illumination as well as displacement mapping. A simple Ambient Occlusion render without the displacement would probably take around 2-4 minutes, depending on AA settings and whether I use the displacement or not. And for reference, without displacement the model is at 8300 polies. With displacement the model's polycount is effectively unlimited.