Thanks for the clarification.  That makes things much easier to deal with in
coming up with a solution for you.  I'll be looking at this later, have to
rush off right now, and quite possibly someone else will add the few lines to
your existing code needed to accomplish this before I even get back.  It's
actually probably only going to be about half-a-dozen lines of code or so.

Trying again - sorry if ends up semi-duplicate posting.

Try putting this code inside of your current _Change() event handler.  Down
near the bottom, probably just ahead of the Exit Sub statement would be a
good place (after that statement wouldn't do much good <g>).

Change the line defining the time of day for the save to be whatever time
you want it to be.

   'variables for the workbook save operations
   Dim originalFullName As String
   Dim newFullName As String
   Dim TimeToSave As Date ' date/time
   
   TimeToSave = "10:30:00 AM" ' change as you want
'put this somewhere down inside of your current _Change code
   If Format(Now(), "hh:mm") > TimeToSave Then
       originalFullName = ThisWorkbook.FullName
       newFullName = Left(originalFullName, Len(originalFullName) -
Len(ThisWorkbook.Name))
       newFullName = newFullName & Left(ThisWorkbook.Name,
InStr(ThisWorkbook.Name, ".xls") - 1)
       newFullName = newFullName & "_" & Month(Now()) & "_" & Day(Now()) &
"_" & Right(Year(Now()), 2) & ".xls"
       If Dir(newFullName) = "" Then
           ' haven't done this yet, so do it now
           Application.DisplayAlerts = False
           'save with the new name
           ActiveWorkbook.SaveAs Filename:=newFullName
           'clear out the existing data
           If Selection.SpecialCells(xlCellTypeLastCell).Row > 3 Then
               Rows("4:" &
Selection.SpecialCells(xlCellTypeLastCell).Row).Select
               Selection.Delete shift:=xlUp
               Range("A3").Select
           End If
           'revert to the old name
           ActiveWorkbook.SaveAs Filename:=originalFullName
           Application.DisplayAlerts = True
       End If
   End If

What it does: if the current time is later than the time you've coded into
it, then it creates a new filename (for use in same folder) and tests to see
if that file already exists, if it does not exist, saves current workbook
with the new name, clears out any information in rows 4:n, where n is last
row used, and then gives the workbook its original name back.

If the modified file already exists in the folder, then it none of this
happens - waits until the next day to write another copy.

I split the build up of the new file name over 3 instructions, just to keep
line breaks here in the forum to a minimum, obviously those could be written
as a single instruction.