Just as a note: if you work 6x12 shifts, you're actually working less efficiently, because you'll be regularly fatigued, make more mistakes, need more rework, etc etc. You might end up with the same net yield as if you'd done 3x6 hour shifts.

(edit: And only if you don't fall asleep at the controls and destroy the factory first. 12 hour shifts are brutal. At least one place I know bans you the next day if you exceed 11h, for your own protection if nothing else)

(edit2: This was documented in the 1st world war when munitions factories that tried to ramp up by increasing shift durations past a certain point ended up hardly improving productivity, but did increase accident and sickness rates to the point that it was starting to hurt the war effort. )