Kick User Off After Inactivity

I picked this code up off this board but it isn't quite working. After 5 minutes it activates the message. However, if no option is selected by the user, it just sits there because it is waiting for a user response and doesn't actually save and close the workbook.


Private Sub Workbook_Open()
Application.OnTime (Now + TimeValue("00:05:00")) - TimeValue("00:00:30"), "Message"
End Sub
Sub Free()
ThisWorkbook.Save
ThisWorkbook.Close
End Sub
Sub Message()

Cuser = Environ("username")
continue = MsgBox("This workbook will save and close in 30 seconds unless you press NO.", vbYesNo, "Hello " & Cuser)
If continue = vbNo Then
Application.OnTime (Now + TimeValue("00:05:00")) - TimeValue("00:00:30"), "Message"
Else
Call Free
End If

End Sub