Problems with creating custom EditorGUI for script

Okay, so I follow the instructions in the section [Extending the Editor][1] for creating a custom Inspector GUI for my script, but I cannot get my GUI to do anything. It shows up, but then nothing works. I'm placing it in the right place and everything!

Here's my code:

 @CustomEditor (DayAndNight)
 class DayAndNightEditor extends Editor {

 function OnInspectorGUI () {
     target.dayLength = EditorGUILayout.IntSlider("Day Length (In Minutes)",1,1,1440);
     
     if (GUI.changed)
         EditorUtility.SetDirty (target);
 }

}

What exactly am I doing wrong? [1]: http://unity3d.com/support/documentation/Components/gui-ExtendingEditor.html