I searched everywhere but I'm not satisfied by the answer. At last I'm posting here to get the answer.
I have two datepicker and time picker textbox which displays 12:00 format with AM & PM.
Here I want to calculate the TOTAL time which includes number of days and given time.
I want to add those time and display it in another text box. I need it in HH:MM format. I don't want seconds as my time picker textbox shows only HH:MM which is enough for me. 
I tried many methods to add but i'm not getting the exact time value.
Below is my HTML code
<input type="date" id="opening_date">
<input type="date" id="closing_date">
<input type="time" class="time" id="garage_out_time">
<input type="time" class="time" id="garage_in_time">
<input type="text" id="total_hours">
Below is my script code
$(document).ready(function () {
function ConvertDateFormat(d, t) {
    var dt = d.val().split('/');
    return dt[0] + '/' + dt[1] + '/' + dt[2] + ' ' + t.val();
}
$(".time").change(function () {
    var start = new Date(ConvertDateFormat($('#opening_date'), $('#garage_out_time')));
    var end = new Date(ConvertDateFormat($('#closing_date'), $('#garage_in_time')));
    console.log(start, end);
    var diff = new Date(end - start);
    var days = Math.floor(diff / 1000 / 60 / 60 / 24);
    var hours = Math.floor((diff % (1000 * 60 * 60 * 24)) / 1000 / 60 / 60);
    var total = (days * 24) + hours;
    var startTime = document.getElementById("garage_out_time").value;
    var endTime = document.getElementById("garage_in_time").value;
    var s = startTime.split(':');
    var e = endTime.split(':');
    var endtime = parseInt(e[1], 10);
    var starttime = parseInt(s[1], 10);
    var min = endtime + starttime;
    var minutes = min ;
    var minhours = Math.floor(minutes / 60);
    minutes = minutes % 60;
    total = total + minhours;
    if(minutes > 9){
    $("#total_hours").val(total+":"+ minutes);
    } else {
        $("#total_hours").val(total+":0"+ minutes);
    }
});
});
Above code is working for some extent BUT for example when I select 8:12 AM to 8:12 PM , the result I'm getting is 12:32 where answer should be 12:00.
 
     
    