In the site admin, go to Company > Locations > (select location) and scroll down to the bottom of the page.
To set your store hours, click on the clock next to the corresponding column to set Open or Close hours, then use the up and down arrows to adjust your hours and finally click on the "Save & Continue Editing" button.
Please keep in mind that hours within the admin use military time, while on the front end of your site the hours are displayed in a more "human readable" format (am/pm).
You can also mark a day as "Closed" or "By appointment only" by checking the appropriate box. To save your changes, don't forget to click on the "Save & Continue Editing" button.