Before you actually start adding blocks of this Add-On to your website, go to your Dashboard (assuming you've installed the Add-On already). On the very bottom of the page (or right hand side menu, if you've opened the Dashboard menu), you will see a lot of links starting with "Sitemap", "Files" et cetera. At the very bottom, "Opening Times" will be added upon installation. You can click this link to enter your default Opening Times.
You will have a page where each day of the week is displayed (7 days - Monday till Sunday), where you can enter your time periods you're open. If you're closed, simply hit "Closed" and you don't need to add any periods at all. Once you're statisfied with these opening times, hit "Publish opening times" at the bottom of the page. Now you've successfully entered your default opening times! You can actually start adding blocks to your website now, using these opening times.
There will be days you are closed most likely, perhaps on News Years Day/Eve for example. Enter these in the "Holidays" section (the link directly under Opening Times, on the right hand side again). Entered dates will mean you are closed thoughout the entire day.
But perhaps you're not fully closed, but closed just a little earlier/later (or opened earlier/later)? Use "Special Openings" instead then. That's the link beneath Holidays (a link directly under Opening Times, on the right hand side again). Enter a date and the time periods of this specific day, and you should be good to go.
Always hit "Publish" or "Save changes" to actually push the changes you made! We do not save anything automatically for you.