That would seem to lead unavoidably to extremely perverse incentives.
Which should mean every company, according to the law (at least in my country, BR)
You've only got about 30-35 valuable hours per week. Beyond that and your time is approaching $0/hour of value.
There are lots of extremely valuable things I can do that don't require deep focus -- like being available to junior engineers to field their questions and keep them unblocked. Even at hour 60 that has significant value.