Use case: I would use this in my Lighting automations and within rule restrictions (I don't use sunset or sunrise as these rely on cloud). This would be super useful particularly in the UK where we observe daylight saving times each year. If such a feature existed I could change one GV value instead of editing many rules twice a year.
No, these don't rely on cloud. There is a built-in astronomical clock. If you don't have an internet connection then your hub clock will drift and need to be manually set. But, if you do have an internet connection it stays with the correct time. In any event, sunrise and sunset times are calculated based upon your location.
Ha! In the US we also observe daylight saving time each year, so you're not alone in that. Except in a few places, including Arizona where I am, we do not change our clocks at all. Having lived with both, I greatly prefer no daylight savings time change.
Adding a time GV would be quite messy and I'm not inclined to want to do this at this time, especially since your need for it is not a true need, but based on a misunderstanding.
Just an update on this: Unfortunately using the hubs Sunset and Sunrise in this scenario hasn't been working out but I wanted to share my simple workaround.
Usually due to cloud cover (that's clouds in the sky... not data centers!) it's sometimes dark enough in the house to warrant motion lighting activating, but due to the "official" Sunset time it can be another 1-3 hours before things kick in. (Note: I have attempted to use offsets and I do not utilise any illuminance sensors).
Quite simply, my workaround to achieve setting custom Sunset and Sunrise times was to use Rule Machine to schedule Evening mode between two manually set times, then go through each Simple Lighting rule and apply the Mode restriction to it.