ISTR something in labor law about no more than 5 hours in a row without a meal break? Or maybe that is just the union contract where I work. (Legally meaningless, since I work for the Feds, but still mostly followed anyway.)
But yeah, expecting people to work (other than in an emergency) an oddball shift like that, is an indicator of piss-poor planning. By the last 2-3 hours of their shift, even for healthy people, their sugar levels will be way low, they will be making more mistakes and getting less work done, and they will be snapping at the customers. Hungry people are cranky people.