Hello,
The iOS version of APT Darkness Clock (APT DC) is now live! It is also free and without ads as the Android app
APT DC allows calculating the Deep Sky Darkness (DSD) time duration, start and end for selected night/location. DSD means, the time suitable for imaging/observing faint objects. With other words when there is no Moon above horizon and twilights are away. Even if you are using top class narrowband filters, there is need to know when the astro twilight ends/starts.
For info, links and QR codes take a look here:
https://www.ideiki.com/astro/MobileApps.aspx
Hope that you will find the apps useful