Man that ATP/Gleim book is garbage, an unfortunately necessary evil that has to be done, it has practically zero relevance to you in your career as a dispatcher, does not help you find solutions or prevent problems, in fact all it does is test your short term memory!
Just treat it like a trip to the dentist, get it over and done with as quickly and painlessly as possible and then with it out of the way get down to learning to become a dispatcher.
The previous poster is right though, get it done sooner rather than later, preferably before you land at your dispatch school, you'll increase your chances of success much more.
Hustle On