<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/08/19/setting-the-open-duration-on-a-menu-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();">

    <mx:Style>
        Menu {
            openDuration: 1500;
        }
    </mx:Style>

    <mx:Script> 
        <![CDATA[
            import mx.controls.Menu;
            import mx.events.SliderEvent;

            private var menu:Menu;

            private function init():void {
                menu = Menu.createMenu(null, xmlDP, true);
                menu.labelField = "@label";
                menu.showRoot = false;
                menu.variableRowHeight = true;
            }

            private function showMenu():void {
                menu.show(50, 50);
            } 
        ]]> 
    </mx:Script> 

    <mx:XML id="xmlDP" source="menuDataProvider.xml" />

    <mx:ApplicationControlBar dock="true">
        <mx:Spacer width="100%" />
        <mx:Button label="Open Menu"
                click="showMenu();"/>
    </mx:ApplicationControlBar>

</mx:Application>