For me, I would guess that I spend 13 hours a day looking at a screen. I think that's just modern life for a lot of people, especially those who work in tech.
It's pretty essential if we're going to have those connected devices in the classroom there is a way to control it.
I would prefer rigorous blocking over teacher control - but reasonably I think it's kind of necessity in a classroom setting.
So, you're absolutely correct that the figure is much higher, and the rest of the article shares potential health and social risks that children (instead of adults) have when they are so plugged in, "modern life" aside. I believe, however, that children are more vulnerable to these risks than us who work in tech all day.
What school has their students be on laptops all day?!
As you get older most exams are done on Linux distro called DigabiOS (https://github.com/digabi/digabi-os) the same distro is also used for the matriculation exams. You boot this off of a USB drive and hope it works well with your own machine.
So I can absolutely see people spending most of their school day on a computer staring at a screen.
I recently rewatched Neon Genesis Evangelion and noticed that in many of the classroom scenes all of the kids had laptops. The anime aired in 1995/1996, but was set in 2015.
As a tech worker I use screens more than them, but I am at least paid OK for destroying my body and can evaluate the trade-offs and adjust my life if needed.