I thought about that, but I wanted to ground the display in the natural cycle of the day. Once you introduce wall-clock time into the design, there are at least two problems that need solving:

1) what's the timezone? 2) what about DST?

The first is quite complex and requires knowing more than just lat/lon. Dates of DST also do change over time according to policy. The only solution I saw for these would to go full IoT so it could talk to NTP servers or have a control interface, and that would ruin the plug-it-in-and-it-just-works minimalism I was going for.