I ran into problem today while updating my Nüvi 2595.
I was initially quoted 2 hours 29 minutes for a full update of all of Europe. The program hung about halfway through at 1:21, when I checked email while it was running using Outlook. I looked in the forums, and saw that others got this hang going by stopping and restarting Garmin Express, despite the warning not to do so.
I did this too. The second time around the three step process was reduced to 2. Initially I was given a time estimate of 2 hours and 29 minutes, which moved up to over 12 hours, and then back down to 2 hours and 20 minutes. Then it went down at faster than real time to 1:31, and then counted down in real time to 1:21.
I checked email again, at which point the time estimate went up to 12 hours, then worked its way down at warp speed to 9:30.
Then all of a sudden, with the progress bar showing 45% or so, Garmin Express reported the update was completed successfully.
I didn't believe it, but I disconnected the Nüvi from the computer, rebooted it. It came up fine. It asked to reboot to install more apps, which also worked.
So the warnings and progress analytics of Garmin Express program is not to be taken too seriously.
There's no reason for this sort of mediocrity in a Windows app in this day and age.