It is correct that the election of a valid 9/80 alternative workweek schedule is limited to 40 hours per workweek, so, for example, employees can’t work 44 hours one week and 36 hours the next week.
All employers are required to designate a workweek and a workday.
The key to establishing a valid 9/80 is to identify a workweek that allows the employee to work 40 hours in each designated workweek. This is accomplished by splitting the day.
One example is to start the 24-hour workday at 12 noon, which results in four hours worked in one day and five hours worked in the next.
The next step is to choose a workweek. If the one day off is a Friday, for example, the workweek will begin at 12 noon on each Friday and run through 12 noon the next Friday. This method results in a correct 40-hour workweek.
Read about a 9/80 alternative workweek, including a sample calendar, in the HR Library.