Quick update.
In order to add longitude, latitude and date to the setup, we have had to remove time to drive the kays and replace it with sun elevation. Keyable properties such as sun col, sky col, fog etc all relate to the sun elevation anyway. As the sun goes up the sky col changes, the haze col shifts and the sun colour becomes less rich. There was a plan to key based on whether it was twilight, dusk, mid afternoon etc but we can't use this approach because the date shifts the sun elevation at different times of the day. Midday in winter and summer have very different sun altitudes and hence different looks. Also the sky textures link to the angles because of the hdr sun, so using sun elevation was really the only way to go.
We currently have this working and I have to say that Kevin has done a great job. In the live edit tool I can set the date and the long/lat. The sun rotation and elevation automatically update with these inputs using accurate real world values. I then key the chosen elevations in the same way I was keying at specific times before. I go to a time I want to key, read off the elevation and change the settings for those. So if I set a key for the sun at 5 degrees at dusk and then change the date, when I move the time slider to dusk on the new date, I will see the same 5 degree dusk I previously keyed. It sounds complicated but it isn't. I'll also set up default keys so you won't be creating from scratch, just tweaking my existing values most of the time.
One thing we are currently adding is code to distinguish between sun rising elevation and sun setting elevation. This way we can key so that dusk looks different to dawn (less moisture in the atmosphere at that time so different colours etc).
We have setup the long/lat for each track, so when you play these in the future, they should have accurate day/night cycles that match the time/date and location. We just need to check that our track exports are all oriented the correct way so that north aligns with +y in the export software.