I did water changes twice a day for 2 weeks when I started my rock...but then I was more interested in keeping the critters that make the the rock "live rock" alive then getting ammonia readings.
When you buy "live rock" all the bacteria necessary to complete the nitrate cycle are already in place. Our job is to wait for all the dead stuff inside the rock to finish decaying and polluting the water, then we need to remove the pollution before algae takes over.
It worked for me anyways, I've cured 4 batches of live rock and the nitrates have always reached 0 in about 3 weeks
*edit* Here's an interesting read
http://forum.marinedepot.com/Topic23945-9-1.aspx