I have not had a regular work schedule or sleep schedule in years.... Currently at the for hospital and work sat-sun-mon 7a-7p from home or at the office. There really is no need for me to sleep regularly at all except certain mondays. I only stay up late usually pursuing some personal interest on an obscure topic, or attempting to complete a task, and wake up early if there is a specific task I wish to work on. What generally leads me to stay up random hours is it is quiet, I can think and work on or enjoy things in peace that others may interrupt.