I thought this was going t be about productivity gains through idle time. It's actually about spending half your time self promoting. It's directed toward researchers, but it applies equally to anyone producing output. The point: do good work, but also promote it or it'll never see the light of day.
I would say it is better to spend all your time productively in what ever you do best. You can get someone else to do the promoting. As a result you spend 100% of your time doing what you do best, programming for example, and someone else spends 100% of their time promoting, which they perhaps do best.
You Should Waste 90% of Your Time<p>"If you don't fail at least 90 percent of the time, you're not aiming high enough." -Alan Kay<p>I think therefore that the expected value of the ratio of time wasted to total time should be x, where x >= .90