Do they operate 24/7?

Even if it is batch process, going from 24 hours to 8 hours is like tripling plant cost vs productivity.

tripling capex vs. productivity, yes, but maybe if capex is small compared to opex, that's a worthwhile tradeoff. the one particular plant i was able to find the answer for does operate 24/7

don't forget wind. there's lots of wind power and very low power consumption at night. it's probably more like 22 hours to 16

They generally will run the cheapest electric rates. They commonly run only the overnight shift when electric is cheapest - it is worth paying the employees that extra money to work the overnight shift. They commonly shutdown the entire month of December for yearly maintenance - when Christmas lights add additional electric demand. They coordinate with the power company for other shutdowns.