You will find the overtime settings under the General Settings that are under the Settings tab in the General section.
Per day overtime
If you do not have overtime on a daily basis (let's say after 8 hours in a day overtime applies), put 24hours.
Add the number of hours per week to be considered in overtime.
Note: This setting is applicable to all employees. It is possible to override this setting per employee under their profile (at the bottom of their profile).