The length of the work week can be defined in the Worktime section in either the Working community or Setting group level settings. The setting can be found in Worktime > Administration > Working community settings / Setting group settings > Work hours > TES.
If the length of the working week is not specified at all in the setting ‘TES work week length’, the default value is 0.
The length of the work week is defined in settings TES work week length and TES maximum hours of work per week. These two values can be different from each other and their difference will automatically be additional work.
It is recommended to use the validity tool when defining the length of work week.
If the length of the work week is not defined before, it can be set without Valid From and Valid To dates, in which case it will always be and always has been valid. 
If an existing value should be changed, the old one must be set to end by adding a date to Valid To -field. Then a new value is added by clicking "Add setting value". The new one will automatically start from the next day of the old one's end date.
Please also check if you need to make any changes to the length of work day settings.