Total Hours from 2 EE Time Select Fields

total.hours.js

<script type="text/javascript">
$(function() {
$('#arrival_hour, #arrival_minutes, #arrival_noon, #departure_hour, #departure_minutes, #departure_noon').on('change', function(event) {
        var arrival_hour = $('#arrival_hour').val();
        var arrival_minute = $('#arrival_minutes').val();

        var departure_hour = $('#departure_hour').val();
        var departure_minute = $('#departure_minutes').val();

        if (arrival_hour && arrival_minute && departure_hour && departure_minute) {
            var today = new Date();
            
            var arrival = new Date(today.getFullYear(), today.getMonth(), today.getDate(), arrival_hour, arrival_minute);
            var departure = new Date(today.getFullYear(), today.getMonth(), today.getDate(), departure_hour, departure_minute);
            console.log(arrival, departure);
            var diff = new Date(departure - arrival);

            var diffHours = Math.floor((diff % 86400000) / 3600000);
            var diffMins = Math.floor(((diff % 86400000) % 3600000) / 60000);
            var amount = diffHours + parseFloat(diffMins/60);
            $('#time_spent').text(amount.toFixed(2));
            $('#hours_total').val(amount.toFixed(2));
        }
    });
});
</script>