Date problem, part 2

I am passing in 3 dates from an HTML page:

<PARAM NAME = "date" Value="04/04/2002 01:00:00AM,04/04/2002 23:00:00PM,04/05/2002 01:00:00AM">

The difference is 22 hours and 2 hours, however when i try to convert it based on the code below, I get

0 0.0
1 13.0
2 720.0

It seems like if they are on the same day it works fine, but when you go to the next day, it should calculate 24.0, not 720?   I try 04/05/2002 03:00:00AM and it just adds 2 on it.

import java.awt.*;
import java.applet.Applet;
import java.util.*;
import java.lang.*;
import java.text.*;

public class graph extends Applet
{
     public void paint(Graphics g)
     {
           int Y1 = 10;
           int Y2 = 350;
           int X1 = 50;
           int X2 = 550;
           int ySpan = 8;
           
          String dates = getParameter("date");
          String data = getParameter("data");
         
          java.text.SimpleDateFormat date_format = new java.text.SimpleDateFormat("dd/MM/yyyy hh:mm:ssa");
         
          StringTokenizer aryData = new StringTokenizer(data,",");
          StringTokenizer aryDates = new StringTokenizer(dates,",");
          int numitems = aryData.countTokens();
         
          String[] arydates = new String[numitems];
          long[] aryDTdiff = new long[numitems];
         
          DateFormat df = DateFormat.getDateInstance();
          for (int i=0;i<numitems;i++)
          {
               arydates[i] = aryDates.nextToken();
               try{aryDTdiff[i] = date_format.parse(arydates[i]).getTime();}
               catch(java.text.ParseException e){};
          }
         
          //initalize them
          float lowVal = Float.valueOf(aryData.nextToken()).floatValue();
          float highVal = lowVal;
          for (int i=1;i<numitems;i++)
          {
             float tempVal = Float.valueOf((aryData.nextToken())).floatValue();
             
             if (tempVal > highVal) highVal = tempVal;
             if (tempVal < lowVal) lowVal = tempVal;
           
          }
         
          //cycle through the Y Coordinate values
          g.drawString(Float.toString(highVal+1.0f),X1-35,Y1+5);
          g.drawLine(X1-2,Y1,X1+5,Y1);
         
          NumberFormat nf = NumberFormat.getNumberInstance();
               
          for (int i=1; i<=ySpan;i++)
          {
               double d = (highVal - (highVal-lowVal)/ySpan) - (highVal-lowVal)/ySpan * i;
               nf.setMaximumFractionDigits(2);
               d = new Double(nf.format(d)).doubleValue();
               float f = (float)d;
               g.drawLine(X1-2,(Y2-Y1)/ySpan*i,X1+5,(Y2-Y1)/ySpan*i);
                g.drawString(Float.toString(f),X1-35,(Y2-Y1)/ySpan*i + 5);
          }
         
          for (int q=(numitems-1); q >= 0; q--)
          {
               g.drawString(Integer.toString(q) + "  " + Float.toString((aryDTdiff[q]-aryDTdiff[0])/1000/60/60),X1+200,Y1*(q+20));
               //g.drawString(Integer.toString(q) + "  " + date_format.parse(arydates[q]).getTime(),X1+200,Y1*(q+20));
               //g.drawString(Integer.toString(q) + "  44",X1+200,Y1*(q+20));
         
          }
                                         
         
          //draw graph layout thingy
          g.setColor(Color.black);
          g.drawLine(X1,Y1,X1,Y2);
          g.drawLine(X1,Y2,X2,Y2);
         
     } // end paint
}// end graph Applet