Not to be cynical, but I bet the devs at NPR are already working on interesting side projects about 20% of their time, because if they don't they quickly become obsolete, and if they are grown ups their managements isn't monitoring them so closely they would even know. It's just that management (often) likes to pretend that they are completely in charge; "giving" devs 20% is sort of like "letting" a teen age son or daughter drink an occasional beer at a party.