Hi Tim, thank you for your reply.
I did get in touch with the plugin developer.
He is suggesting to
place that function just before the markup is printed. So in the Widgets widget() method
I am not entirely sure what it means, but will look into it.
As per the plugin, I am outputting a "we are open" or "closed" message in the footer (plugin takes the WP timezone as a reference).
I thought about using the WF exclusion tool, but don't really know if, for example, I can exlude the whole footer.