Measure Time Taken To Find File & Open

I am trying to measure how long it takes to locate a file the user wants to open. Eg., from when they click File|Open to when they click the "Open" button in the Open dialog box (after they have navigated through the directories to find their file).

I have approached this by using a class module and withEvents. This uses the Click event to trap when they have hit the File|Open button from the File menu and timestamp it.

class module: EventFileOpen

Public WithEvents cbOpen As CommandBarButton

Private Sub cbOpen_Click(ByVal Ctrl As Office.CommandBarButton, CancelDefault As Boolean)
MsgBox "File open started at: " & Now()
End Sub

Private Sub Class_Initialize()
Set cbOpen = Application. CommandBars.FindControl(ID:=23)
End Sub

Private Sub Class_Terminate()
Set cbOpen = Nothing
End Sub..........