Night Light auto schedule uses timezone instead of geographic coordinates — incorrect sunrise/sunset for locations far from timezone center

Summary

Night Light "Auto" schedule calculates sunrise and sunset times based on the system timezone (e.g., Europe/Moscow), not actual geographic coordinates. This gives incorrect results for users living far from the timezone reference point.

Example

Both use Europe/Moscow, but sunset differs by 1h40min. A user in Makhachkala will have Night Light turn on 1h40min too late and turn off 30min too early.

Expected behavior

Auto mode should either:

1. Use the coordinates from night-light-last-coordinates gsetting (when manually set by user via gsettings or gammastep/redshift config), falling back to timezone-based estimation if no coordinates are set
2. Or allow selecting a city/coordinates in the Night Light settings GUI
3. Or at minimum document that Auto mode is timezone-based and recommend Manual schedule for accurate times

The night-light-last-coordinates key exists in org.cinnamon.settings-daemon.plugins.color schema but is only used as a cache for GeoIP data — unused when the user sets it manually or when GeoIP is unavailable.

Current workaround

Use "Manual" schedule with custom times, or set coordinates via:

gsettings set org.cinnamon.settings-daemon.plugins.color night-light-last-coordinates "(42.9, 47.5)"

(these coordinates are currently ignored by the auto schedule calculation)

System

• Cinnamon 6.6.7
• Linux Mint 22.3 Zena
• X11

Start by tracing Cinnamon's Night Light Auto schedule implementation and the org.cinnamon.settings-daemon.plugins.color schema, especially night-light-last-coordinates; reproduce the timezone-versus-coordinate difference with the provided gsettings value. Confirm the intended behavior with maintainers, then verify that the agreed coordinate fallback, GUI support, or documentation change produces accurate or clearly communicated scheduling.