It was always 75%. The choice is: predictably over time, or when burnout occurs & all at once (for each engineer.)
C-bro wants predictability.
Telling your developers to bugger off for 1 week every month will never work out. They still need to be at the office, but they can pursue learning, help with planning (this is critical), or focus on other development tasks they actually want to make.
Ah, when the linked article suggested developers go "surfing" I thought it meant in the sea, not the web.
I think that was the intention. I just don't believe it will work out.