I'd think the key point here is focus.
Short periods of very focused work is much better then a whole day of unfocused work. I guess that's true. And since you can't work hard and focused for eight hours, the elite players split it up in two time periods with some relaxation in between.
Short-term focus is why I fell in love with and still use Leo Babauta's GTD-related idea of MITs (Most Important Tasks). See links at bottom.
Each morning I set 3 tasks (sometimes 4 or 5 if I absolutely have to and they're small) that would make me feel good about the day if I finish. I write them in an otherwise empty text document, order them by importance, and start working on the first one.
These tasks can be large or small, sometimes even just "send this email" that will take 15 minutes to write, but is really important to send off. This also works great when working from home, because even if the environment is different, I can still feel productive if I at least finish those 3 things.
If I finish the 3 things early, I assess my energy level and either finish the day with organizing emails or reading up on stuff or other low-effort tasks, or I tackle one last MIT if I feel up for it. The point is to prioritize short-term focus of the 3 MITs instead of looking at the potentially endless list of todos I could keep picking from all through the day.
