Public Const mydelay As Integer = 10
Public Const mycount As Integer = 3
Public Const myfolder As String = "\autobackup\"

Public Sub callmelater()

    For Each mybook In Workbooks
        Call savethisworkbook(mybook)
    Next

    Application.OnTime Now + TimeSerial(0, 0, mydelay), "callmelater"

End Sub

Private Sub savethisworkbook(mybook)

    If mybook.Path = vbNullString Then Exit Sub

    On Error Resume Next
       MkDir mybook.Path & myfolder
    On Error GoTo 0

    myfilename = Left(mybook.Name, (InStrRev(mybook.Name, ".") - 1))
    mybook.SaveCopyAs mybook.Path & myfolder & myfilename & "_" & Format(Now, "YYMMDD_hhmmss") & ".xls"

    With Application.FileSearch
        .LookIn = mybook.Path & myfolder
        .fileName = myfilename & "_??????_??????"
        .FileType = msoFileTypeExcelWorkbooks
        .Execute SortBy:=msoSortByLastModified
        If .FoundFiles.Count > mycount Then Kill .FoundFiles.Item(1)
    End With

End Sub