How to calculate date difference (in hours, days and months) between two known dates using user input (datetime)?

Question

There are two datetime fields, which are filled by the user. I need to calculate the difference between them in hours, days and months. All examples I found are with dates that are entered in JavaScript or JQuery, but not from user input. My code is not working. I think I use the selection wrong.

---

    function getDD () {
    var adate = $(document.querySelector('input[id="d04"]').value);
    var adatems = adate.getTime();

    var odate  = $(document. querySelector('input[id="o02"]').value);
    var odatems = odate.getTime();

    var hms = 3600000;
    var dms = 86400000;
    var mms = 2628002880;

    var difOA = odatems - adatems;

    var oah = Math.round(difOA / hms);
    var oad = Math.round(difOA / dms);
    var oam = Math.round(difOA / mms);

    $('#r1').val((oah));
    $('#r2').val((oad));
    $('#r3').val((oam));
    }

    $(document).ready(function() {
    $('input[name= a_date]').blur(function(e) {
    $('#r1; r2; r3').val());
    getDD();
    $('input[name= o_date]').blur(function(e) {
    $('#r1; r2; r3').val());
    getDD();
    });
    });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input id="d04" type="datetime-local" name="a_date">a_date
    <br />

    <input id="o02" type="datetime-local" name="o_date">o_date
    <br />

    <input id="r1" type="text" name="o-a_ hours" readonly="true" placeholder="Diff in Hours"/>o-a_hours
    <br />

    <input id="r2" type="text" name="o-a_ days" readonly="true" placeholder="Diff in days"/>o-a_days 
    <br />

    <input id="r3" type="text" name="o-a_ months" readonly="true" placeholder="Diff in months"/>o-a_months  
    <br />