ขอสอบถามเกี่ยวกับโค้ดการคำนวณการหาระยะห่างของวันที่หน่อยค่ะ

<SCRIPT language="javascript">
function TimeDriff()
{
	var diff;
	var start = new Array(3);
	var end = new Array(3);
	var st = document.getElementById('start').value;
	var en = document.getElementById('end').value;

	//Thai DateFormat 15/08/2552 - DD/MM/YYYY

	//Split Start -> Date/Month/Year
	start[0] = st.substr(0,2);
	start[1] = st.substr(3,2);
	start[2] = st.substr(6,4);

	//Split End -> Date/Month/Year
	end[0] = en.substr(0,2);
	end[1] = en.substr(3,2);
	end[2] = en.substr(6,4);

	end[1] -= 1;
	start[1] -= 1;

	end[2] -= 543;
	start[2] -= 543;

	StratDate = new Date( );
	EndDate = new Date( );

	StratDate.setDate(start[0]);
	StratDate.setMonth(start[1]);
	StratDate.setFullYear(start[2]);

	EndDate.setDate(end[0]);
	EndDate.setMonth(end[1]);
	EndDate.setFullYear(end[2])

	if(StratDate.getTime( ) < EndDate.getTime( ))
	{
		diff = EndDate.getTime( ) - StratDate.getTime( );
		diff = Math.floor(diff / (1000 * 60 * 60 * 24));
	 }
	else if(EndDate.getTime( ) < StratDate.getTime( ))
	{
		diff = "0";
	}
	else if(EndDate.getTime( ) == StratDate.getTime( ))
	{
		diff = "0";
	}

	if(diff==undefined)
		document.getElementById("tmdiff").value = "";
	else
		document.getElementById("tmdiff").value = diff;
}

</SCRIPT>
<b>Calculate Time Between </b><p>
<table border="1" cellspacing="0" cellpadding="2">
<tr><td>Time Start : </td><td><input type="text" id="start" name="start" onChange="TimeDriff()"></td></tr>
<tr><td>Time End : </td><td><input type="text" id="end" name="end" onChange="TimeDriff()"></td></tr>
<tr><td>Time Diff : </td><td><input type="text" id="tmdiff" name="diff"> Days</td></tr>
</table>