hours of duty

例句：

1. 1. The police officer has been on duty for twelve hours.
   这名警察已经值班十二个小时了。
2. 2. The doctor needs to work more hours to save the patient's life.
   医生需要加班才能挽救病人的生命。
3. 3.The factory is closed for the day, so the workers have had no hours of duty.
   工厂今天关闭，所以工人们没有工作时间。