This is a very unique request from one of my clients, an Excel file that shows a message (or run certain macro if you modify it) at certain time.
That means the file has to stay open and not closed. It also has the option to show the count down timer or not.
What you need to do?

1. Open the file and enable macros
2. 2- Set the date and time in cell D3 (zero hour)
3. Click (On)
4. Go do anything else until the time is up and Excel will show you a message.
   To see the counter actually counting down, set D11 to 1 (also cehck the comment on that cell)
   You may also interrupt the timer any time by clicking (Off)

This file is provided as is, for any further changes or modifications, please contact me