He tells you literally and exactly what he means: his "point is purely about the effective output of an individual". Emphasis is mine on effective output. His opponents argue that there's a peak in productivity, such that if workers wanted the greatest chance at stopping the asteroid, they should choose to only work 35 hours a week. He argues that this peak either does not exist, or is way more than 35 hours.
It makes more sense when you think of salaried vs hourly. Because hourly people are so obviously useful on long hours that companies will pay 50% more to have them there.
