You don't need to work every minute. All you need to do is to not waste it away. So go skiing for a full day is still considered making good use of the current moment than reading reddit. For me, I think not wasting my life away means I'm either contributing to the society by working or I'm making my self a better person by working out, skiing, reading books etc.
I think you have to be fully engaged in any activity you are making. If you want to relax, relax in a full paced way. Not worrying about the work you have to make.
If you must work, work in a fast-paced way, and make the job done.
The worst kind of works is the one multi-tasked. You dont get in a 'flow' state that is necessary for the most jobs people here in hacker news makes.
I can see that being good practical advice for getting things done, but I'm less sure it's good (or at least universal) life advice, especially to follow all the time. My model for a good day spent is a lot of intermingled puttering around, reading, thinking, relaxing, working, to make unexpected connections between things, find new angles on problems, and generally understand how everything fits together better. Like the way a Douglas Hofstadter book "flows". I really, really dislike the "work-hard / play-hard" lifestyle; just doesn't work for me at all.
Yup, living only in the current moment without worrying about the past or upcoming moments solves this too. Easier to get into work flow, and much more fun when skiing!
