datetimepicker_script.js

<script type="text/javascript">
    jQuery(document).ready(function($) {
        var $field = $('#new_admingeneratorbundle_activity_start_participants');

            var $widget = $('#'+$field.attr('id')+'_widget');
    var config = {"locale": "nl","format": "DD-MM-YYYY HH:mm","useCurrent": false,"sideBySide": true,"stepping": 5,"icons": {"time": "fa fa-clock-o","date": "fa fa-calendar","up": "fa fa-arrow-up","down": "fa fa-arrow-down"}};

    $widget.datetimepicker(config);
    $widget.data("DateTimePicker").date(moment("22-07-2015 13:46", "DD-MM-YYYY HH:mm"));

    var copyValue = function() {
        var date = $widget.data("DateTimePicker").date();
        if(date == null) $field.val('')
        else $field.val(moment(date).format("DD-MM-YYYY HH:mm"));
    };

    $widget.on("dp.change", copyValue);
    $widget.find('a.s2a-date-btn').on('click', function(e){
        e.preventDefault();
        e.stopPropagation();
        $widget.data("DateTimePicker").show();
    });
    $widget.find('a.s2a-clear-btn').on('click', function(e){
        e.preventDefault();
        e.stopPropagation();
        $widget.data("DateTimePicker").date(null);
        $widget.trigger("dp.change");
    });
    $field.closest('form').on('submit', copyValue);
        });
</script>