This could be by devoting several hours to a creative endeavour or just an hour.
But the key is that it is a routine and it is every single day. No day can be skipped, because once a crack appears in a routine, the routine itself falls apart.
It is all too easy to allow distractions to determine one's schedule instead of dismissing them altogether.
This slice was critical to their success. In some cases it may have been the smallest part of their day, but it still determined their life.
For anyone to find the success they crave, they must structure their day into a daily routine, as all of the famous creative people have done so for centuries.