It looks like the link to the claim of shortening the work day is based on how schools for children aren't as long as the adult workday so I think your second question is already being applied right now.
"In the LinkedIn post, Grant was weighing in on an Atlantic article about the time gap between when school and work days end, a bane for many parents. But it's not the first time Grant has given his stamp of approval to less work with more productivity."
Not really. In my area, the school day is 8:00 AM to 3:00 PM. Teachers typically arrive by 7:30 AM and leave around 3:30 PM - and then do grading and other work activities in their evenings. Where do you cut 25% from that? Who watches the kids - especially in some communities where single parent households are the norm? If the state provides daycare, the money has to come from somewhere, and school budgets are stretched as is.
The workday reduction is a bit hand-wavy - it sounds good on the surface but when you get into the nitty gritty.
"In the LinkedIn post, Grant was weighing in on an Atlantic article about the time gap between when school and work days end, a bane for many parents. But it's not the first time Grant has given his stamp of approval to less work with more productivity."