Rotation is measured in degrees, and there are 360 degrees in a full rotation. A full rotation is 60 seconds. Therefore, every second, we want to move 6 degrees (360/60).
This expression: time*6
will gives us a smoothly-sweeping second hand.
To make it click once per second, we can use posterizeTime(), which forces Ae to update the property value at a different frame rate than the comp. Using a value of 1 tells it to update at one frame per second, for your perfect staccato second hand: