try below code
// start time and end time
var startTime = moment("12:16:59 am", "HH:mm:ss a");
var endTime = moment("06:12:07 pm", "HH:mm:ss a");
// calculate total duration
var duration = moment.duration(endTime.diff(startTime));
// duration in hours
var hours = parseInt(duration.asHours());
// duration in minutes
var minutes = parseInt(duration.asMinutes())%60;
alert (hours + ' hour and '+ minutes+' minutes.');
check fiddle here
http://jsfiddle.net/nil4you/gs69Lv5x/
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