The bacteria that process ammonia develop faster than those that process nitrite. Usually on a fishless cycle, it takes about twice as long for the nitrite to drop as it did for the ammonia to drop but part of that is because you are adding more nitrite (in the form of ammonia that is transformed into nitrite) than you did ammonia to start. The best thing to do is continue the water changes to keep it as low as possible and keep monitoring it. It shouldn't take too much longer.