The first step would be for you and your sisters to "stay at a particular schedule for a period of time, at least one to two weeks, and then when you make the shift, shift forward, from say an eight-to-four shift to a four-to-midnight shift," says Thomas Freedom, MD, director of the Sleep Disorder Center at Evanston Northwestern Healthcare in Evanston, IL. "The shift has to do with the way our sleep rhythm works; it's easier to stay awake and go to bed later."

In addition, there are several stimuli to try when going through the process of "resetting your internal clock," says Dr. Freedom. "Stay away from bright lights and keep things dim near bedtime. Conversely, when you get up, make things very bright; open all the windows and turn on all the lights if it's daytime. It's important to get exposure to light."

It's all about following what Dr. Freedom calls "the basic, good practices of sleep. Keep the bedroom quiet and, if needed, wear a sleep mask or earplugs. Beyond that, if there's still a problem, his advice is to "avoid over-the-counter medicines and seek a sleep professional. The American Academy of Sleep Medicine will help you find a local sleep center." Just go to www.sleepcenters.org.