As a kid I remember visiting relatives with farms and ranches in Utah and Wyoming. None of them ever ate lunch or dinner. To them lunch was "dinner" and dinner was "supper".
But, as you said, meals were at a certain time every day. Especially "dinner" at noon because everything was scheduled so they and all the hired hands stopped and ate at the same time. "Dinner" was the big meal of the day; "supper" was a light meal after the work day was done. Breakfast was always more than just a bowl of cereal or piece of toast because you had to make do with the energy from breakfast all the way to "dinner" at noon. Coffee breaks? No such thing as any break got in the way of the workday that was pretty much dawn to dusk.