Actually, in general, high school was the most demanding part of my life, so far as long stretches of time go (sure, I've had the odd week or month that's worse). And I was a pretty bad slacker about things like homework (given the time demands even with that lax attitude, I think I'd have gone actually-crazy otherwise).
Middle-aged now. Nothing's been as rough as high school, or even close. And I had it pretty easy (no significant bullying issues or anything like that, stable home life)
I'm conflicted on this, mostly because that after school time was very valuable to me, much more than being able to sleep in a little more. This was extra true in the winter, when the sun set by 5pm. I also recognize that not everyone to be as easily up and awake that early in the day.
And no, it wasn't some ancient history either.