Hi Jim,
Sorry for missing your first post.
Unfortunately, in DayBack Classic there's no way to change how long the built-in undo dialog remains to show.
However, you could technically override this message bar with your own that shows for a longer period of time.
The cascading events functionality here is an example of how to do that with
the showMessage functionIt will take some customization to make it work for your solution, and
implementing event actions is a little different in DayBack Classic.
Since DayBack just calls the "Submit Event From WebViewer" FileMaker script to actually write back the changes to FileMaker, you could keep track of the changes in a global variable, then give your users a button somewhere that would run a FileMaker script to undo the changes that were applied.
Since the new DayBack supports app actions, you could store the event object and revertObject as a global in the web viewer and give users a button in the calendar to perform the undo at any time. Unfortunately, this isn't possible in DayBack Classic as app actions aren't supported.