Depends what one considers “work”; if you’re only counting focused, active coding work then there are places where 4 hours is the max you’re going to achieve of that anyway.

I count work the contracted time I need to be available/tied to my employer. Doesn't matter if I'm doing focused coding or not, it's still work because I can't be paragliding or swimming in that time, I need to be at the office or near my laptop, so it's not leisure, it's still work time.

But let's say it's only counting "focused work", 4h/week is huge stretch, unless we're competing in slacker olympics.