Check for time function

Hello all...I have an issue with one of my java script functions that
I'm hoping someone can easily help with. I have a web based application
that we use to create/sign up for overtime. When we have holidays we
require our employees to sign up in 4 hr increments for the times we
post. I'm having trouble creating a time slot that ends @ 12am. 12pm
and all other hours work fine for start/end times. however 12am causes
problems. My actual script code for this function is below. Someone
help!!!

<SCRIPT language="JavaScript" src="frmvalidation.js"
type="text/JavaScript"></SCRIPT>
<script language="javascript">
    function checkValidHoliday(value)
    {

        if (value=='Y'){
            hourblock.style.visibility ='visible';
        }
        else{
            hourblock.style.visibility ='hidden';
        }
    }

    function checkHoliday(frm)
    {

        if(frm.txtIsHoliday.value=="Y")
        {
            strFromDt= new Date(frm.txtLimitDate.value);
            strToDt= new Date(frm.txtLimitToDate.value);
            FromHr=parseInt(frm.txtLimitFrom.value);
            FromAMPM=frm.txtLimitFromAM_PM.value;
            ToHr=parseInt(frm.txtLimitTo.value);
            ToAMPM=frm.txtLimitToAM_PM.value;

            if((FromAMPM=="PM") && (FromHr!=12))
                FromHr=FromHr+12;

            if((ToAMPM=="PM") && (ToHr!=12))
                ToHr=ToHr+12;

            var fromDt= new
Date(strFromDt.getFullYear(),strFromDt.getMonth(),strFromDt.getDate(),FromHr,0);
            var toDt= new
Date(strToDt.getFullYear(),strToDt.getMonth(),strToDt.getDate(),ToHr,0);
            //alert(toDt + " " + fromDt);
            //alert(FromHr + " " +ToHr);

            var HolidayBlock=(parseInt(frm.cboHolidayHours.value) * 360 * 10000)
;
            //alert((toDt-fromDt) + " " + HolidayBlock );

            if((toDt-fromDt)== HolidayBlock)//14400000)
                return true;
            else
            {
                alert("Please select "+ parseInt(frm.cboHolidayHours.value) +" Hour
Block only for Holiday!");
                frm.txtLimitFrom.focus();
                return false;
            }
        }
        return true;
    }
</script>