Yes Dan, but EPN is a rather old type of film. New generation slide films perform mostly better in reciprocity. Most older films are not recommended above 10 seconds (colorshift indeed). Kodak always delivers reciprocity figures and filter corrections with their films. If not, I would take EPX (or -Z?) and start with 2 stops correction (+2 is for 100 seconds, but there's a logarithmic series involved here: 1, 10, 100, the next step would be 1000 seconds), so that would be 12 minutes. Half a stop down for bite in the slide: 9 minutes. No problem if there aren't any bees around.