Do you have an instant read or probe thermometer? The chicken at it's thickest, most meatiest point needs to hit at least 165 degrees F. That's really the only sure fire way of knowing since time can vary depending on oil temp, temp. of the chicken when added to the oil, etc. etc. One thing you do want to do is to let the chicken warm at room temp. before adding it to the oil so that it won't bring the oil temp. down too far.
"Boldness has genius, power, and magic in it."
Johann Wolfgang Von Goethe