Hi Bear, we just finished cycleing a 46 gallon and it took about 12 days of 5+ nitrite readings. Then the next day it was zero. We did fishless cycling with that tank, so we did not worry about fish exposure. I have a 10 gallon which is cycling with fish in it I was impatient and bought fish thinking the other tank was at the end of the spike was hoping to leave them in a couple of days then they ended up with Ick so I am treating that tank for ick while it is cyclling with the fish still there. I also am worrying about my fish in there with the high nitrite levels. I just keep doing water changes, I've been doing 2 a day to try and keep it from being too bad for the little guys.
Good luck, I hope this helps I know how frustrating it is.
If you're cycling, then patience is a virtue (along with water changes). If not then either a)get more oxygen into the water, B) add Stress Zyme or some other bacteria-introducing stuff, or c)check/fix amount of food given or stocking level.
I currently just finished cycling my 33 g tank and it took about 3 1/2 weeks, when I had the nitrite spike it took about a week for it to drop to 0 and during that nitrite spike I did a 15% water change every other day and at the end of the week I did a 25% wc and the next day the nitrite drop at 0 and my fish were not affected during the cycle and they're all doing great. Just be patient, It will eventually drop at 0