Pressure cooking (including the time to bring up to pressure, pressure cooking, and pressure release) can save you about 2-6 of those hours. Depending on who you talk to, it's either almost as good or perhaps better than simmering for several hours.
Highly agree with this. I was gifted an electric pressure cooker recently, and it has been a revelation for home stock making. It makes truly excellent stock in around 60-90 minutes all up.
