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.
If you read through Hamming's statements, and my reflections on them, you can see that it is not as simple as just promoting - it is specific recipes about how to do so effectively, and how to avoid certain mistakes.
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.
It's not always possible. PR firms are expensive. They also can't promote to a mostly technical audience. That's why you should give talks about your research/development, blog/tweet, post on sites like this. I've found that especially with open source projects, once you get the word out others will be more than happy to be your projects' "technical evangelists" because they love using them.
That being said, if you're a company, can afford a PR firm and you have produced something worth promoting, it usually makes sense to pay others do promote. The Submarine article by Paul Graham really opened my eyes on this: http://www.paulgraham.com/submarine.html (ever wonder where feature stories in mainstream magazines about start-ups, showing happy hackers solving technical puzzles on white boards come from?)
However, I've also seen companies suffer because they've hired sales, marketing and PR staff on "easy" VC/parent company money before they had a working product.
The Alan Kay quote does not say you should waste 90% of your time, Kay says you should fail 90% of the time. It is only wasted time if you don't learn from your failures.
Further, the quote in the original post from Hamming is that "at least 50% of the time must go for the presentation." Hamming does not call preparation and presentation "waste". Reading the Hamming quotes, I find nothing that indicates he thought being friendly, conforming, making, or giving presentations was wasted time.
On the contrary, Hamming spent quite a bit of time criticizing his contemporaries for wasted effort (his words) by ineffectively swinging their egos rather than working within the system (or judiciously bypassing the system).
@gvb the use of the word waste stems from the fact that many technical people (previously including myself) make the mistake of thinking that the time Hamming is talking about spending on presenting your ideas is waste.