https://apps.garmin.com/en-US/apps/97352d10-5316-4e9c-8399-288228d3dcb2
Just uploaded and approved. Only tested in simulator so far, if anyone wants to test on a real device I'd be happy to hear how it looks and works.
The code is also available, with sunrise equation based on wikipedia
https://github.com/tradespoke/SunriseSunset/blob/master/source/SunriseEquation.mc