Math calculations can be performed with the Expressions feature, but there’s not currently an official way to use dynamic schedules.
There’s a feature request for being able to use variables in the Delay block which I believe would be needed for what you’re looking for. Feel free to cast a vote and bump the thread with your use-case.
The last piece would be how to schedule this and I suspect that just doing it once or twice a day would be sufficient as you could have the rule trigger every day at 12:01 and then have it calculate how long you need to wait until your desired time.
I would also add that the sunset / sunrise are not exposed as variables directly, but there’s several other ways you could get that value.