Setting definitions of work time units
When you're not using a standard 40 hour work week or eight hour work day, you can customize your project's standard units of work-per-time using the Project Unit Conversions inspector.
Your work day may be any number of hours. These conversion factors determine how to add up hours into the larger units.
The effort conversion factors don't actually change the working hours for the project, just the way durations are entered and displayed. To change the working hours, visit the work week section of the Calendar view.