jquery date time picker minDate / maxDate issue - date

Question

the code below was working perfectly fine before but recently I noticed that the minDate/maxDate isn't working anymore, strange because I didn't make any change on the code. I have been struggling with this for a few days now, it's annoying.
I am using this -- http://mugifly.github.io/jquery-simple-datetimepicker/
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript" src="http://mugifly.github.io/jquery-simple-datetimepicker/jquery.simple-dtpicker.js"></script>
<link type="text/css" href="http://mugifly.github.io/jquery-simple-datetimepicker/jquery.simple-dtpicker.css" rel="stylesheet" />
<input type="text" name="start_time" id="start_time">
<input type="text" name="end_time" id="end_time">
<script type="text/javascript">
$(function(){
$('#end_time').change(function() {
$('#start_time').appendDtpicker({
"futureOnly": true,
"closeOnSelected": true,
"dateFormat": "DD/MM/YYYY hh:mm",
"minTime":"07:00",
"maxTime":"23:00",
maxDate: $('#end_time').val() // when the end time changes, update the maxDate on the start field
});
});
$('#start_time').change(function() {
$('#end_time').appendDtpicker({
"futureOnly": true,
"closeOnSelected": true,
"dateFormat": "DD/MM/YYYY hh:mm",
"minTime":"07:00",
"maxTime":"23:00",
minDate: $('#start_time').val() // when the start time changes, update the minDate on the end field
});
});
// trigger change event so datapickers get attached
$('#end_time').trigger('change');
$('#start_time').trigger('change');
});
</script>