Arrival time is hours off

You car's GPS system is close to 8 years old... Compare that to running a Google or Apple map app on your phone that gets real time updates hundreds of times a day and will route you around traffic and construction projects to make sure you get to your location as quickly as possible. If your life depended on it, which of these two options would you choose?

 

Which route alternative did you select: Fast, Short, or Ecological?

If you picked Short, what were the times listed on the other two alternatives? I have seen some very large differences between them, due to the Short choice being routed over comparatively slow gnarly roads, though not as large as you saw here. The presumed driving speed across any 'Short' route dirt roads can be very slow.

Unless you or a previous owner applied the overpriced navigation update, the map database is more than 8 years old. Have any of the roads that you used, been built or significantly improved since then? Or did the recommended route have any apparent errors? Though since you merely "mostly" followed the suggested route, rather than "exactly," you may not have directly encountered any such crawling-speed road.

Then don't discount the possibility of map database errors affecting your route. Smartphone nav apps, or even regularly updated nav devices, are much more likely to have these errors weeded out.

 

The nav time is independent of the time on your dash.

The time on the dash, you can set to anything, using the H and M buttons.

The nav time comes from the GPS satellites, and the nav also knows more or less what time zone you are in, so it can show the time as local.

But it doesn't automagically know whether daylight saving time is currently active or not. There's a place in the setup -> clock screen on the nav screen where you turn DST on or off. So if you forget to fiddle with that twice a year, you can have your nav times (and estimated arrival times) look one hour off.