text input datepicker enddate after startdate validation - validation

Question

I have 2 input boxes, startdate and enddate. I am trying to force the user to select a date in the 2nd input box that is after the date in the first input box. This will be validated on ajax save.
Everything including the isvalid works great in ie but does not work in FF or opera.
In FF and opera no matter what the date before or after start date, it just keeps displaying the isValid: "Must be after start date" message and not validating.
Does anybody have any ideas why, or a solution using the datepickers so it modifies the minDate on the 2nd datepicker.
Here are the buttons for the ajax modal:
buttons: {
'Save': function() {
if($("#new_request_form").valid()){
// do stuff if form validates
submitFormWithAjax($("#new_request_form"));
$(this).dialog('close');
} else {
// do stuff if form does not validate
}
},
'Cancel': function() {$(this).dialog('close');}
},
Here is the date check to make sure the enddate is after the startdate:
jQuery.validator.addMethod("isValid", function (value, element) {
var startDate = $('#startdate').val();
var finDate = $('#enddate').val();
return Date.parse(startDate) < Date.parse(finDate);
}, "* End date must be after start date");
$("#new_request_form").validate({
rules: {
days: "required",
hours: {
required: true,
number: true,
digits: false
},
startdate: "required",
enddate: {
required: true,
isValid: true
}
},
messages:{
days: "Required",
hours: {
required: "Required",
number: "Numbers Only"
},
startdate: "Required",
enddate: {
required: "Required",
isValid: "Must be after start date"
}
}
});
var $ac_start_date = '<?php echo $ac_end_date ?>',
$ac_start_date_flip = '<?php echo $ac_end_date_flip ?>',
$ac_start_parsed = Date.parse($ac_start_date),
_today = new Date().getTime();
// For Opera and older winXP IE n such
if (isNaN($ac_start_parsed)) {
$ac_start_parsed = Date.parse($ac_start_date_flip);
}
var _aDayinMS = 1000 * 60 * 60 * 24;
// Calculate the difference in milliseconds
var difference_ms = Math.abs($ac_start_parsed - _today);
// Convert back to days and return
var DAY_DIFFERENCE = Math.round(difference_ms/_aDayinMS);
// do initialization here
$("#startdate").datepicker({
dateFormat: 'dd-mm-yy',
changeMonth: true,
changeYear: true,
yearRange: '0:+100',
minDate: '+1d',
maxDate: '+' + (DAY_DIFFERENCE + 1) + 'd'
});
// do initialization here
$("#enddate").datepicker({
dateFormat: 'dd-mm-yy',
changeMonth: true,
changeYear: true,
yearRange: '0:+100',
minDate: '+1d',
maxDate: '+' + (DAY_DIFFERENCE + 1) + 'd'
});
}, 'html');
return false;
});
}
function submitFormWithAjax(form) {
form = $(form);
$.ajax({
url: form.attr('action'),
data: form.serialize(),
type: (form.attr('method')),
dataType: 'script',
success: function(data){
}
});
return false;
}