Working hours are a way to better plan your schedule, and let others know where you'll be.
To enter your working hours, go to your profile page. The quickest way is via the profile button in the top right of the screen.
Then scroll down to My Work Week. Here is where you can set blocks of time for where you will be and at what time. To do this, scroll down to Add My Working Hours.
After clicking Add My Working Hours, you can set where you will be, at what time, and on what days. You can add multiple blocks of time, but as of this article they cannot overlap.