Log into the Partner Tool and select "Opening Times" at the top of the page.
Once opened, choose the location you want to set the opening times for and select the appropriate day of the week, and then the time in the dropdown (the format is HH:MM).
Click the "Submit" button to save all changes. Please note: There is no confirmation window that pops up once the opening times have been saved, so please make sure that they are correctly updated. To do so, you can refer to your location profile page (this can be found in the top right corner of the partner tool under "Location Webpages").
Once saved, you can update your existing opening hours by selecting the dropdown again, or clicking on the red delete button to remove them entirely.
Please note: There is currently a technical error when adding the opening hours in the partner tool in that it does not load if any language other than English is selected. However, there is a simple workaround for this. When adding in the Opening Times tab, be sure that English is selected in the top right as the language.