ObjectARX 2004 SDK had this nice C++ sample on adding tray items to the status bar and displaying balloon notification in one of those tray items. I have migrated this sample project to work on AutoCAD 2015 and you can download it here :StatusBar
To build this sample, place it under \samples\editor folder in ObjectARX 2015 SDK path. Here is a sample code snippet to display balloon window from that sample :
// Create the bubble notification message, and callbacks.
CString strMsg(_T(" Notification" ));
"HyperText Here" ,
To control the time the balloon will be displayed, please run the "TRAYSETTINGS" command and set the display time.