These working solutions last for much longer than indicated if you are willing to accept wrong contrast, colour cross over, fog (oxidized PPD goes up in pH), reduced Dmax, speed loss. None of these issues are of major concern if you go the hybrid route, that's why people can use C-41 for months. While few here do optical RA-4 enlargements, slide projection is still something people look into, therefore you may want to apply more stringent process control with E6.