Here's the straight skinny for NWA GOLD Elite members: 2 days prior means by midnight of the 3rd day prior to flight, meaning for a Wednesday flight the upgrade is done by midnite Sunday.

Now for the real deal. Since we live in different time zones, one would think that those in the eastern zone would get upgraded first, and those in the Pacific would be last. It doesn't work that way. It looks like all the Golds in my example above are "ranked" and the upgraded together. You can verify this by going to the NWA.COM view travel arrangements place on SUNDAY around 8pm & you'll see that it has already been done for you.