If you spend 4 hours/24 hours on your phone then every 20X you'll have lost 3.33... X.
I think the author is using year and waking-years but it doesn't parse well for me because you don't get close to 20 waking-years for every 20 years.
https://support.apple.com/en-gb/guide/deployment/depf4ab94ef...
https://en.wikipedia.org/wiki/Palm_OS
Perhaps focussing on productivity and helping users like these devices did/had to instead of being consumption devices is a way to explore?
As a bonus, if you're a parent and have kids it'll be very useful for them.