Turn the handwheel toward you until the bottom timing mark is at the top of the timing gauge.
At this point, if the machine is timed correctly, the hook should be just behind the needle.
If the hook is not in proper position, rotate it so that it is. This is why we left the screw loose in the OHS (Oscillating Horizontal Shuttle ) crank. Once you have the hook directly behind the needle with the timing mark in the proper place on the gauge, tighten the screw in the OHS crank
I do tend to do this with the machine on its side so that I have the best access to the screw in the OHS crank.
This process does take patience and it does require very minute adjustments. Keep the screw loose enough so that you can rotate the hook, but not so loose that it requires a lot of effort to tighten it. If you jostle it too much you could disturb your position of the hook and the needle. It might take multiple tries but I manage to do it and I am not a professional (sewing machine mechanic, that is)
So that's timing the hook of a Singer 66.