Listing tries to pre-fill most information based on your Google location. However, here you can simply edit, remove, or add opening hours.
By clicking on Add hours, you can add multiple opening hours per day. This is relevant whenever you close during the day and re-open (i.e. Siesta).
Search engines such as Google My Business have options other options that you can also apply in Listings; such as:
Open 24 hours
In this section of "Opening hours," If you set the hours to be from 00:00 to 24:00, just like in the picture below your business will be set to "open 24 hours"
*IMPORTANT* If you manually change your opening hours in your Google My Business account Listings will not overwrite them later. Please keep in mind should this have been the case you must first change the opening hours in Listings to false ones, sync, and then change them to the correct opening hours again in Listings and then sync.