We're so remote the sun never sets on our group, so the definition of "workday" is pretty fluid, so yes, "when they're not busy" is a good partition. Otherwise, as the other child comment says, there is a pride in supporting effort. I don't necessarily benefit directly from the projects they may work on. Like others have said, I can't coerce them to do write open source code. But I definitely benefit from their improved or sustained skills. You have to find differentiators to make such decisions. Are you arguing that I should ignore signal or that open source contributions are an invalid signal, or the use of the signal itself is immoral, by some definition of "immoral"?