Hi there,
I have just reviewed the information on the NCSBN website regarding this.
http://www.ncsbn.org/pdfs/2006_Candidate_Bulletin.pdf
See page 4 of this pdf - the paragraphs entitled 'Registration Process Overview" and "Registration time limit". The NCLEX examination registration period is indeed a year, but this purely the time within which your BON must determine your eligibility to take the exam. Once they have done so, you can apply for the actual ATT. The site also says: "Once a candidate is made eligible, he must test within the validity dates printed on the ATT."
My ATT has validity dates on the top righthand corner: 4/1/2006 - 6/30/2006. This is a period of 90 days or 3 months.
The ATT also says on page two: "You must schedule your examination within the validity dates listed above. These dates cannot be extended, regardless of the reason."
This is why I told Leslie that the ATT is valid for 90 days. Perhaps this only applies to foreign-trained nurses taking the NCLEX? In which case I apologize for misleading you. But take a look at this online doc for yourself and see what you think.
Blessings and best of luck,
Elleann