js查询距离某一时间的时间

<SCRIPT language=javascript>
<!--
//document.write("");
function show_date_time(){
window.setTimeout("show_date_time()", 1000);
BirthDay=new Date("5/20/2011 11:40:00");//起始日期
today=new Date();
timeold=(today.getTime()-BirthDay.getTime());
sectimeold=timeold/1000
secondsold=Math.floor(sectimeold);
msPerDay=24*60*60*1000
e_daysold=timeold/msPerDay
daysold=Math.floor(e_daysold);
e_hrsold=(daysold-e_daysold)*-24;
hrsold=Math.floor(e_hrsold);
e_minsold=(hrsold-e_hrsold)*-60;
minsold=Math.floor((hrsold-e_hrsold)*-60);
seconds=Math.floor((minsold-e_minsold)*-60);
span_dt_dt.innerHTML=daysold+"天"+hrsold+"小时"+minsold+"分"+seconds+"秒" ;
}
show_date_time();
//-->
</SCRIPT>