"A Jewish-calendar day does not begin at midnight, but at either sunset or when three medium-sized stars should be visible, depending on the religious circumstance. Sunset marks the start of the 12 night hours, whereas sunrise marks the start of the 12 day hours. This means that night hours may be longer or shorter than day hours, depending on the season." Their "watches" are divided into 3 hour increments. The first watch would be 6pm-9pm. The second watch would be 9pm-12midnight. The third watch would be 12am-3am. The fourth watch would be 3am-6am. The daylight hours are divided the same way.