Typically short. A few hours with pulmonary exposure. A few days with the typical bite exposure (bubonic plague).
2 to 6 days. The incubation period (time between exposure to the bacteria, by a bite or by inhaling the germs, and the development of the first symptoms) for bubonic plague is 2-6 days, and for pneumonic plague is 2-4 days. Less commonly, the incubation period for pneumonic plague can be 1-6 days... which is important, because pneumonic is fatal if treatment isn't started within 24 hours of first symptoms.