What do you mean by "not working" and "giving an error"? If Excel is
giving an error message, what is it and on what line of code? If
nothing is happening, does your data have an end time within 3 hours?
If it doesn't, nothing will happen. Are you waiting 15 minutes?

I tested the code (with "00:00:10" rather than "00:15:00") with the
following in the ThisWorkbook module and it worked fine for me.

Private Sub Workbook_Open()
StartTimer
End Sub


Hth,
Merjet