There are also a lot of in-game factors that can influence the time it takes to compute shadows. It usually takes about two minutes for me (then again I have a high-end Gateway FX series desktop which I recommend if you don't have the time, money or experience to build a custom rig of your own), but I recently built a track that took twelve minutes. It had a ton of spotlights at night. Tunnels will increase computation time, so will overhangs, enclosed spaces, and narrow canyons.