Staying late during payroll processing

I'm a recent graduate who got the position of a junior payroll member for a middle eastern airline. I don't have much experience as this is my first full time job and the only reason they hired me is because of the goodwill i made through multiple internships with the same airline.

Our payroll team consists of 6 members and every month when its time to start the payroll process, our manager tells us to sit for extra hours even if we have nothing to do. According to him, payroll will be more efficient if we act as a team and we should leave work together. Because of this every month from 21st to 27th we sit from 9am to 1am/2am everyday and its like running in a marathon for 8 days straight. Its difficult to argue since everyone does stay together and no one complains either.

Is it normal to stay this late when its payroll week and if not how do i change my boss's mindset.