We use the bili check meter at 24hrs of life and before discharge ( usually early in the morning the day of discharge). I work night shifts so I keep the lights in the room dimmed. I have not heard that it is necessary to get an accurate reading. We too use a graph to determine if the newborn has jaundice. I have though accidentally miss calculated the hours before and the pediatrician pointed out the error. I found a good app for OB nurses that determines the hours of life of baby, called Nurse Aid.