We prompt once on reboot if your location is not set at all.

We deliberately round to the nearest 0.1 degree for privacy (>5 mile box), but typing in a nearby city or airport code is usually fine.

I'd bet on latitude, myself. If the object of the game is to more-or-less match daylight hours, it's nice to know what daylight hours are going to be.

Most people don’t move around significantly. One way to find this is by detecting networks: if I’m plugged into Ethernet or connected to the same wifi, I’m probably at the same place. Please do not ask me for my location.

We only prompt if your timezone offset changes (traveling), or if you've never set things up. Something in the parent's configuration is triggering "never set". We have not used BSSIDs for this because some corporate and campus users roam between hundreds of APs, so it would be much more invasive (or we'd have to chat on the network to figure out that nothing had changed).