I have formatted your program so that it is more comprehensible:

import java.util.*;
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class CDF extends MIDlet implements ItemStateListener
  {
  private Display display;
  private Form fmMain;
  private DateField dfTime;

  public CDF()
     {
     display = Display.getDisplay(this);
     // The main form
     fmMain = new Form("Testing..");

     // DateField with todays date as a default
     dfTime = new DateField("", DateField.DATE_TIME);
     dfTime.setDate(new Date());
     // Add to form and listen for events
     fmMain.append(dfTime);
     fmMain.setItemStateListener(this);
     }
  public void startApp ()
     {
     display.setCurrent(fmMain);
     }
  public void pauseApp()
     {
     }

  public void destroyApp(boolean unconditional)
     {
     }
  public void itemStateChanged(Item item)
     {
     System.out.println("itemStateChanged");
     }

  }

If this were an AWT program I would say
fmMain.setItemStateListener(this);
should read
fmMain.addtemStateListener(this);
But since it is a MIDLET, I don't know.

I would also check that if you are supported to an get an Item rather
than an event at your listener. That is not how AWT works.

I would check that Forms generate ItemStateChanged events not some
other sort. That is the usual problem in AWT.

Sorry I can't be more help since I don't have midlet experience.

Nothing wrong with your code. Running it, as soon as you change the
time or date and hit Save, itemStateChange is called.
--------------------
Paul Hamaker, SEMM, teaching ICT since 1987
http://javalessons.com