I can definitely answer this...as I live in Golden and have been recently commuting back and forth to Castle Rock for a listing I just closed.
Good weather, not rush hour = about 45 minutes
Good weather, rush hour = about 1 hour 20 minutes (getting through the congested area of C470 and breaking loose at about Santa Fe)
Bad weather, not rush hour = about 1 hour 20 minutes.
Bad weather, rush hour = up to 2 hours (C470 out west can get bogged down on snowy days with many accidents, as well as, once you hit I-25 going south -- not a fun drive at all)
Any reason why you would want to live in Castle Rock, if your job is in Golden. I know I may be a little bias as a native of Golden, born and raise and my children now being born and raise (oldest graduating from Golden High)....
Please contact me if you would like to talk more about the lovely neighborhoods of Golden, I can give you many reasons why I love calling it home.
RE/MAX 100 - The Deitz Group