I don't see anything wrong with your code, and I can verify that it should work if it matches what you've posted. Just make sure you don't have any spelling or capitalization mistakes in your actual code.
$(function(){
$('.emltdp-emltd-test').datetimepicker({
timeFormat: 'hh:mm tt',
});
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.3/themes/smoothness/jquery-ui.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.3/jquery-ui.min.js"></script>
<script src="http://trentrichardson.com/examples/timepicker/jquery-ui-timepicker-addon.js"></script>
<link rel="stylesheet" href="http://trentrichardson.com/examples/timepicker/jquery-ui-timepicker-addon.css" />
<input class="emltdp-emltd-test" />