Act I of The Phantom Tollbooth plays with the concept of time. This is important in the novel, as the whole book is intended to make us think about ideas and concepts that we had previously taken for granted. In this section, the clock tells us that time is important, but mostly depending on what you do with it. This shows that the author believes that time is only relevant when we look at what we are doing with it. It also suggests that the author believes time to be relative.
One example of the author's perspective on time is the comment that he makes about seeing things differently when you are at different stages in life. "Then your head keeps changing its height and you always see things in a different way? Why, when you're fifteen things won't look at all the way they did when you were ten, and at twenty everything will change again." This shows that the author believes time to be relative, and to be an important factor when looking at the world.
Another example occurs when Milo receives a package that reads "To Milo, who has plenty of time." This shows that the author considers time to be an opportunity. Moreover, he suggest to us that the opportunity should not be wasted.