Wow this makes me want to buy an Apple Watch! In the military knowing first-light and last-light, down to within a few minutes, is essential daily. I have an app on my phone that tells me sunrise and sunset, but as the article describes these aren't the same thing. I also have a very expensive top-of-the-range Garmin watch and even that just tells me the less useful sunrise and sunset, which makes me suspicious it's…
https://www8.garmin.com/manuals/webhelp/fenix66s6xpro/EN-US/...
Or check the Solaris watch face which shows civil twilight, nautical twilight, astronomical twilight, and night.
https://apps.garmin.com/en-US/apps/0e019a96-aeb3-4aaf-81ed-4...
Above subject to which device you have.