Executing a macro at a defined time

[celtic warrior]

I have a worksheet that is used to update daily events. I currently have a macro which is operated manually to send a copy of the worksheet to a defined mailing list.
I would like to automate this process so that the worksheet is mailed at a defined time each day.
I tried the following:

Private Sub Workbook_Open()
 
    Application.OnTime TimeValue("16:16:00"), "Mail_sheets"
 
End Sub

But it doesn't seem to work?

CW