it depends on how much of an over feeding it is, and how well your biological filter has been established.
How much Live Rock do you have in your tank? Usually, you want to aim for 1-2 pounds per gallon. The bacteria that live inside of it breaks down ammonia into nitrites then into nitrates. The first two are really toxic to fish while the nitrates are not until they get well over around 40ppm.
Like biff said, get ready to do a water change. Just incase. Have the salt water mixed up and just ready. If you dont need to, you will have it ready for your next scheduled maintanance.
Brian