Building up the bacteria to break down the Nitrites usually takes twice as long as building up the bacteria to break down Ammonia. (Don't quote me on this but this is what I have experienced) So lets just say that it took a week for the Ammonia to go from 5ppm to 0ppm, then relatively speaking it will take up to 2 weeks for the Nitrites to go from 5+ppm to 0ppm.
I'm currently having the same issue with my Nitrites (they are off the charts). They have been like that for at least a week now but I'm not worried about it. Just make sure to keep adding ammonia so the bacteria have something to feed on because you don't want to lose any of those.
Just be patient, it may take upwards of a month for a tank to fully cycle, maybe even longer. Be patient
Thanks Fish Fanatic, I have been cycling for 6 weeks now, Ammonia is going within 24 hours or there abouts, Nitrites still way above 5ppm and no increase in Nitrates for 2 weeks...
Long time no update, anyway, all is well, had a week of ammonia and Nitrites down to zero in 12 hours, done a 50% water change and last weekend got some fishes
3 Pearl Angelfish and 5 Gouramis
still some more fish to get, but having to explain to the better half why Brakish fish are no good for our tank