I was thinking of allowing lat/long in config.ini. As long as we're correct within a couple of hundred miles that should be enough, so someone could put their home address in there, or maybe use whatever value the last point in a route called 'home' has.

I actually looked at the cold-start process of the SV6 when there is no backup battery. As it doesn't know time or place, it randomly scans for satellites. Once it finds one it pretty much immediately has a reasonable approximate time estimate and starts downloading the almanacs for all satellites. Once it has the almanac of the current satellite, it assumes this satellite is located approximately directly overhead and from that location estimate starts scanning for other visible satellites. As I was testing from inside the satellite it saw first was in fact at the horizon, so it really had a hard time finding my real location.

But a reasonable time estimate is something that we seem to get pretty much as soon as we hear from any single satellite, while location takes a lot more time and effort as the location estimate affects which satellites are assumed to be visible.