I've seen U2 eight times over the years, and was in the GA for three of those: Atlanta on the Vertigo Tour, and both Belfast and Dublin on the I&E Tour. For Atlanta, my good friend and I queued all day, starting around 10am. We didn't get into the inner circle, but managed to get one or two people deep on the Edge's side. For both Belfast and Dublin, though, I didn't bother queuing. If the weather wasn't so wet and cold (this was later in November in 2015), maybe I'd have queued up some just for the social experience; but, the weather emphatically ruled even that out for me.
With the show this summer, I'm in the GA for Pittsburgh, and I probably won't get in like before 4 or 5 pm, though I'll wait and see based on fan reports from some of the shows before mine (as a random aside, I do have a seated ticket for the second night in Chicago, too).