Hello! We are here to help educate, share our experiences, and help you to be successful. As such there has been some sound advice already given by others. I would like to build on it and let you know that....
It is much faster to use some other ammonia source in a fish-less tank for the cycle. A dead deli shrimp works great here. That way you can create high levels of ammonia which in turn allows for larger amounts of bacteria to grow in a shorter amount of time.
Using live fish to cycle a tank is not humane. By having a fish in a tank that is cycling is harming the fish and causing it to suffer. Even low amounts of ammonia burn the gills of fish which affects the amount of oxygen they can take in. They tend to die due to lack of oxygen. Suffocation. It is a slow death that causes the fish to suffer. Ammonia can cause damage to fish gills at a level as small as 0.25 mg/l. Ammonia is extremely toxic to fish and your CUC at 0.5 mg/l. This is not something that can be seen.
If you do cycle tanks w/fish, the proper way to do it is to monitor the ammonia levels to make sure they don't get high, keep on top of testing of ammonia levels and keep on top of water changes (sometimes water changes need to be done daily to keep the ammonia levels low). Low amount of feeding helps. This type of tank cycling can take longer b/c it will take more time to build up the bacteria in the tank that breaks down ammonia, nitrite and nitrate. All these levels need to stay low for the safety of the fish in the tank.
When cycling tanks with fish in them can take a LOT longer then using the deli shrimp/ fishless method of cycling. This is b/c with a fish you should be keeping your ammonia levels very low, which in turn is not building up high levels of nitrites or nitrates and thus bacteria. You essentially will be building up your bacteria levels very slowly. Much slower then in fishless tanks where you can really get high levels of ammonia, nitrite, nitrate and thus bacteria.
Lastly, cycling with fish can be done, but should be done humanely. And if done correctly, the fish isn't being harmed, and you should expect the cycle to take a lot longer. Testing ammonia should happen daily and if levels are above 0.25 mg/l, then water changes are recommended to bring the levels down.
Keep on top of testing ammonia daily.
And as a rule of thumb, ammonia will usually drop by about the same fraction of water that is changed, so a 30% water change will reduce ammonia by 30%. However, if there is a source of ammonia in the aquarium, it may rapidly rise again. In an ammonia "emergency" much larger water changes may be appropriate.
References:
http://reefkeeping.com/issues/2005-06/rhf/index.php#tab2
http://reefkeeping.com/issues/2007-09/rhf/index.php
http://reefkeeping.com/issues/2007-02/rhf/index.php
http://reefkeeping.com/issues/2005-06/rhf/index.htm
Ammonia in estuaries and effects on fish. Eddy, F.B. Environmental and Applied Biology, University of Dundee, Dundee, UK. Journal of Fish Biology (2005), 67(6), 1495-1513.
http://reefkeeping.com/issues/2007-02/rhf/index.php