If you assume you have a huge reserve of capable people, then that will clamp down on wages, but as a manager you still want to optimise the productivity of the employees they have.

Extreme overtime doesn't sound like a good idea. May as well hire 2 shifts of people and pay them half as much; aim for higher per-hour performance. 9-9-6 isn't going to get you very much per hour of labour time, the employees will be zombies.

4 shifts of people will get you 24 hour 7-day coverage if you want continuous production if that is what the business needs. Just hold per-hour pay as constant as possible using the reserve of willing workers as leverage.