Start with your favorite childhood book. I choose Curious George because I enjoyed reading them as a child, and because the book is thin...more on that to come.
This is the clock mechanism that I purchased for around $6.
Notice the length of the part circled in green. If you want the mechanism to go all the way through the book, you will need to choose a thin book like I did. If not, you will have to...
...make some modifications to the book. For example, taking off the back cover might help. You may also have to take some pages out. Or you may have to use only the front cover.
Now find the middle of the book using a ruler, or the point at which you want the clock to be positioned at. Mark it with a pencil or pen.
Now take a drill bit that is similar in diameter to the clock mechanism and drill through the book at the marks. You may have to clean the edges up with an Exacto knife.
Now insert the mechanism and either place double sided tape on the back of the book cover, or glue the whole box to the back of the cover.
I used double sided tape and it sat flush with the back of the book.
My clock kit didn't come with instructions, so I used this simple diagram to put it all together. Took less than a minute! http://www.bearwood.com/media/mini_quartz_clock_instructions.jpg
You can place numbers on the front cover if you'd like, but I like to see the artwork...
And there you have it, a childhood book clock! Enjoy!