The timing depends upon the source of ammonia. Is it a continuing source or a one-time deal? Most people don't believe in using damsels any more because of the risk of killing them, but they would provide a continuous source of ammonia. If you put in uncured live rock, it would build up to a peak value of ammonia added to the water, then it would tail off to zero as the curing proceeds. Most tanks complete the cycle within 4-6 weeks. You may be very close to it completing. Once the nitrite starts to come down, it goes to zero within a couple days. Test regularly. I never measured that high of nitrates in my tank at any time. I did have high ammonia, followed by high nitrite, but when I started checking the nitrates (did not check these until the nitrite started down), they were zero. As long as your nitrates return to near zero at the end of the cycle, that is what counts. If they don't, then start looking for a source of that nitrate.