Private Sub Workbook_Open()
' Check to see if data in cell Z1 on Sheet1 is today, and if so, exit
If Sheets("Sheet1").Range("Z1") = Date Then Exit Sub
' Exit if not currently a Monday
If Weekday(Date) <> 2 Then Exit Sub
' Run your code below
' ...
' Update date in cell Z1 on Sheet1 and save file
Sheets("Sheet1").Range("Z1") = Date
ActiveWorkbook.Save
End Sub