I cycled a 75 gallon a few months ago, seeded with live rock. It took less than a week before my ammonia started dropping. My nitrites were through the roof for just about 2 weeks. I left to go out of town on friday afternoon, and dosed with ammonia and my nitrates were literally off the charts on the API master kit. When I got home on sunday the nitrite test water was as blue as the sky. This is what I did when the water didn't turn purple.
Nitrites take FOREVER to drop compared to the ammonia, but when the drop, they drop fast. Patience young grasshopper, patience.