If you have ammonia or nitrite above 0.25ppm, then the emergency this causes for your fish *trumps* all other considerations related to percentage water changes. By not immediately doing a large enough series of water changes to reduce either of these toxins to below 0.25ppm, you leave your fish at greater risk than would be caused by any negative effect of a large change. When you see a number as large as 1, you should do a 50% to 70% and you can do another just as large as soon as an hour later.
~~waterdrop~~
Agree with above post. You need to be doing at a minimum 50% changes when doing a fish in cycle. You need to be testing your water at least 2 times per day to check for traces of Ammonia.