To update the office hours that display to your students in the Course Information block, you'll need to enter your Profile.
Click on the dropdown menu where your name and picture are located at the top right corner, and then click Profile.
Click Edit profile under User Details to access your profile settings.
Scroll down to the Other Fields section to find the box labeled Office Hours. Enter your office hours information in that field.
When you're finished, click the Update profile button at the bottom of the page.