Sounds like #NoKids rather than #SpainBrain. I'm sure it sounds like I'm being pithy, but you fall into line when your kids get home at 4 and you want to spend time with them before they go to bed at 8. Maybe his point stands in some sense, but once you add kids into the mix it quickly becomes "9-5" again or "burning the candle at both ends."
There's also an argument that's been made that kids go to school too early in the day and school start time should be postponed to later in the morning, because they need more hours of sleep.
I suspect the problem is that teens just stay awake FAR LONGER than is advisable perhaps to maximize their free unstructured time at night and to minimize the crushing grind of the mornings?
I expect that if the school start time was shifted to 9am, the kids would just stay up until 5AM instead of only 3AM.