Which is weird because it's pretty straightforward to work out if you need sunscreen or not:

  * Is it any month other than May-August?  
  
  * Is it after 10am or before 4pm?  
  

If you have very light skin you might want to increase the timeframe by an hour.

And if you really want to optimise your sunscreen usage and not use it if you don't have to, the real-time UV index from ARPANSA is the way to go (https://www.arpansa.gov.au/our-services/monitoring/ultraviol...).

All other apps simply display the expected UV index given the time of the day and the day of the year.