You set the timing light to 0 if you're using the marks on the crank. If you want to advance the timing beyond what the marks on the crank indicate, then you set your timing light to however many degrees you want to advance, and then use the same mark ont he crank pulley. Or, you can disregard the red/brown marks alltogether, and just set your timing light to howeve many degrees you want your timing set at, and then set it to the white TDC mark. Since the timing light accounts for the advance, setting the timing to the TDC mark will mean that your timing is at TDC, plus whatever the setting ont he light is.