please help me with this code the subtract part won't work because in my box it just shows -(time here)

<script language="JavaScript">
<!--;
function doTime() {
if (document.check_time.time.value=="") {
document.check_time.real_time.value="";
}
else {
var t = new Date();
var new_time = t.getTime();
real_time = document.check_time.time.value - new_time;
document.check_time.real_time.value=real_time / 3600;
}
}
//-->
</script>

never mind i figured it out