Excellent question. I was recently stationed in Okinawa, Japan as a Corrections Officer for 3 years. My work day would consist of 24 hours shifts. This is because of the standards for the Marine Corps. Throughout the day, my duties mainly involved interacting with prisoners. Ensuring the plan of the day is followed while providing supervision to the prison. I did get to sleep most nights and had an amble amount of time to consume my breakfast, lunch, and dinner.
You are always prepared to be highly alert & aware (which over time, if not maintained every day may make you prone to potential injury or compromise) and you work to make the environment is as safe as possible through a sense of duty, fairness to all & an understanding of both inmate as well as other human behaviors.
Next, you look for signs of potential danger to both the inmates through self-harm or by harm to others as well as watch for problems aimed at you and your fellow officers as well as the public.
Always remember the inmates have AL DAY & NIGHT to study you, fellow officers and weaknesses within the correctional settings, which if exploited may place others at risk.
Again, one of the most important and lest glorified roles in public safety