I thought that I would have to wait for a certain date to come around once a month or so for the exam, but that is not the case. You get your ATT from the board you are testing for and then you go online to pearsonvue and register to take the exam. Once I got there, it popped up a page with the next week listed and times every 30 minutes during the day to test. It was much simpler than I had anticipated. I got ATT on Friday and registered for NCLEX the following Thursday. It was that easy. You do it when you want to, not at the mercy of the state.
ATT is issued from pearsonvue once they get the OK from the state that you meet requirements. if trained in the US then generally you can register with pearsonvue at the same time as you register with the state BON. If trained outside the US we generally advice you to wait for the BON to give the go ahead to register