Private mLastOpenDateTime As Date
Public Property Get LastOpenDateTime() As Date
If mLastOpenDateTime = 0 Then mLastOpenDateTime = Now
LastOpenDateTime = mLastOpenDateTime
End Property
Public Property Let LastOpenDateTime(dte As Date)
mLastOpenDateTime = dte
End Property
Private Sub Workbook_Open()
mLastOpenDateTime = Now
End Sub
'Appel dans un module :
Sub truc()
Dim t As Date: t = ThisWorkbook.LastOpenDateTime()
MsgBox Format(t, "dd/mm/yyyy hh:mm:ss")
End Sub