As many as possible, so I can look at the different studies, try to understand and learn from the information, and make my own informed decision on which opinion I hold.How many books and articles do you need. This forum is not the only source of knowledge.
...but we need to be careful how we get information, because that Fritz information seems to be primarily for freshwater considerations (at least far more than for saltwater) based on other studies by other researchers.
I still see no harm in leaving the cycle until nitrites are no longer present in order to be safe, but this does not answer whether or not nitrites are toxic, which was the original question.