It is easy for a professional comedy writer to advocate making definitive time and space boundaries in your day to enable creative thinking, but before you completely dismiss the possibility that John Cleese is actually a voice of corporate reason, take a listen to this video excerpt from a several years old lecture that he gave.
In the full lecture, Cleese references a British psychologist's study of the "tortoise mind, [which is] a slower, less focused, less articulate, much more playful, almost dreamy" side of ourselves that must be allowed time to roam in order to be creative.
And what does Cleese really think is the enemy of creativity? "The widely held, but misguided, beliefs that being decisive means making decisions quickly, that fast is always better and that we should think of our minds as being like computers...The pressure on managers at all levels to act quickly is enormous." Cleese acknowledges that while we need to be able to multi-task, and let our "hare brain" dominate, we have to carve out time to balance our thinking with our tortoise mind. The book, and Cleese's application to business, are detailed more in this New York Times article.