I can see how someone could assume that the length of a test gives a more valid result, but in this case I don't believe it's true. This is a case where the computer is our friend. NCLEX questions are rigorously tested out before being used in the part of the exam that "counts" (although the tester never knows whether the question is a "real" or an "experiemental" question. The computer has an enormous database of questions to draw on, with a required minimum number in each of the clinical areas (med/surg, pediatrics, psych, maternal health, and so on) and areas of clinical skill: assessment, intervention, evaluation, etc. The questions each have an assigned degree of difficulty, and mastery at a certain level of difficulty is required in order to pass the NCLEX. The computer starts you out with an "easy" question; if you get that one right you get a harder one. If you get that one right you get a harder one still; if you miss it your question difficulty reverts back to the previous level of difficulty. The computer continues testing until the tester demonstrates a consistent level of mastery, and then moves on to another area for testing. This way, a candidate can quickly demonstrate mastery, by answering correctly the questions at the highest level of difficulty, without having to waste time answering a bunch of easy questions that most likely will be answered correctly. This method of testing is called Computer Adaptive Testing and is used for many standardized tests such as the GRE, as well as licensure exams.
Does it work? Well, my experience was that out of my nursing school class, only three classmates didn't pass the NCLEX--and they were exactly the three who had no business possessing a license until they gained either more clinical expertise, more life knowlege, or more plain common sense. I would say the NCLEX computer test did a bang-up job.
BTW I took my NCLEX at 8:30 am on Sept. 11 (Yes, that Sept. 11) and there was a power failure during the exam in which all the lights went out, the computers all shut down in the middle of the exam, and we had to stand outside on the sidewalk for half an hour while they figured out whether we were under attack, someone was a little trigger happy, or just what. I passed with 75 questions. Just a little pressure