Is it whenever the cache expires? Or is it once a day? Week? Basically I don't want to call it wastefully when it is not needed.

I checked between yesterday and today and the min/max dates remain the same. So I am guessing the results don't change (Unless someone adds a new film with a release date in that rage. Which I am not that bothered about.) until the date range changes.

So I guess I am asking when do the date ranges change?