If my memory serves, push the knob through the sheathe to adjust the time. Or maybe its pull, I forget. I know its spring loaded.
Get this... 12 volts to that clock was tapped directly off the ALT' gauge w/ no fuse, and chassis grounded like most everything else. 12 volts applied should cause a "tink" sound which comes from a set of points on a ratchet mechanism that wind the clock so it runs about 4 minutes before another "tink". Adjusting the time shown backward or forward very slightly adjusts to the clock to run faster or slower.