If you were the person who originally created your annual leave calendar, or have been set up as an administrator then you will see a cog icon in the navigation menu.
Click the cog to enter the settings menu.
You will initially be taken to the Company settings menu where you can configure a number of things about how your company is set up.
One key piece of information here is the days on which your company works.
Tick the boxes next to the days/periods on which your company works, and specify the standard working hours of the company.
You can also provide the starting day of the week (eg. Monday), whether the company takes leave in days or hours (the allowance unit) and the company standard "hours per working day" information.
When you're happy, press Save
All of this information can be overridden for individual employees, for example part-time workers, but this is where the company default settings are provided. To override the working week information for individual employees go to the Settings->Employees screen and click on the 'Schedules' button for the employee you want to change.