I believe you have to have 2 years or a set number of hours working with a hospice in order to take the exam unless that have changed it. I have had my CHPN for 2 years now and it was probably one of the hardest test I have taken. Honestly I would wait and work for a hospice and get the experience. Reading about it is one thing and the experience is quiet different and reading books won't help you much for that test. Also your employer may pay for the test as my has. Good luck.
The HPNA requires 2 years exp. The practice book is pretty easy compaired to the actual test. You may want to look into a review class too. It helped me a lot. You don't have to be certified to be a hospice nurse though, and if you get on somewhere they may help you pay for it. Good luck.