<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/07/23/setting-the-amount-of-time-that-a-tool-tip-is-visible-using-the-tooltipmanager-class/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"> 

    <mx:Script>
        <![CDATA[
            import mx.managers.ToolTipManager; 

            // milliseconds (default 10000)
            ToolTipManager.hideDelay = 2500;
        ]]>
    </mx:Script> 

    <mx:ApplicationControlBar dock="true">
        <mx:Label text="Mouse over the Button below to see the tool tip." />
    </mx:ApplicationControlBar>
    
    <mx:Button id="button" label="click me"
            toolTip="I'm a fabulous tool tip." />

    <mx:Label text="The tool tip will disappear after {(ToolTipManager.hideDelay/1000).toFixed(1)} seconds." /> 

</mx:Application>