Check the server_file once an hour for changes and pop-up a notification if it has.

File_differs

1. Copy both files into your user dir (C:/users/<username>)
2. edit the "server_file" path on line 4 of file_differs.bat to use the network file location of your excel sheet
3. Save the edits
4. Click your Start button
5. Type "cmd" and hit enter
6. In the cmd window, type "file_differs.vbs" and hit enter.

file_differs.bat

@echo off
setlocal EnableDelayedExpansion

set server_file=\\server\file\path
set compare_file=%USERPROFILE%\file_differs_compare
set task_name=monitor_excel_sheet

schtasks /delete /f /TN %task_name% > nul
schtasks /create /TN %task_name% /sc hourly /tr "%USERPROFILE%\file_differs.vbs" > nul

fc /b %server_file% %compare_file% > nul
if errorlevel 1 (
    for %%a in (%server_file%) do set mod_time=%%~ta
    msg * "%server_file% updated @ !mod_time!"
    cp %server_file% %compare_file%
)

file_differs.vbs

Set WshShell = CreateObject("WScript.Shell")
WshShell.run chr(34) & "%USERPROFILE%/file_differs.bat" & Chr(34), 0
Set WshShell = Nothing