Sometimes the duration of a lucid dream is dependent on the scenario you find yourself entering into. My longest and most vivid lucid experiences have occurred when I enter a relaxing, or even dull, scenario with few, or even no, DC's to distract me. Sometimes its the luck of the draw. Also , when I get lucid I try to avoid getting my superman mode on as flying has a tendency to wake me up (but i must admit flying is great fun!) Good luck to you...