To set the personal working hours for a specific employee, 

1) Go to the Company screen. To access the Company screen, you may tap on the company logo on the home screen.

2) Tap on the option "Employees".

3) From the Employee List, tap on the employee that you want to update his personal working hours

4) Enter User Profile screen, scroll down and search for the "Working Hours/Days", tap on it 

5) Tap on the "Personal" tab and change based on your need.

Here is the full video of how to update the employee working hour.