That seems like overly 'business' thinking. People as numbers. While necessary on some level. I've found the best performers don't work any specific number of hours, but actually employ a 'chop smarter, not harder' mentality.
Some of my best people work a 30 solid ( dense ) hour week. Those are heads down, no distraction hours. No Facebook, no podcasts, just technical design and code. I don't enforce it, they just do it on their own. As long as they deliver, I want them out of the office, into the gym, outside, whatever the fuck they want, so they don't burn out.
And I'm happy with it because they always stretch and deliver, on time. And their code is tight, thoughtful and consequently maintainable.
As for finding people who exhibit those qualities. I ask them to solve a problem and see how their mind works. If it's thorough, thinking about error handling, documentation, etc., then that's a winner. I then use their Github code to determine seniority and go from there.
Ironically those with the most hunger and passion to learn and excel did not go to top-tier schools. It doesn't take much to figure out why.