My Seder is Longer than Your Seder: How Late Must Your Seder Go?

Is there a minimal time until which the seder has to go? Is there an obligation to continue engaging in the mitzvah of סיפור יציאת מצרים after the Seder ends? We know that כל המרבה הרי זה משובח - the more discusses the Exodus the more praiseworthy he is but does מצות סיפור יציאת מצרים have a minimum shiur?