U2FanPeter
Rock n' Roll Doggie Band-aid
This just seems to be somebody's speculation.
Somewhat uninformed speculation, too, since the second Chicago show is far more likely to be on the 14th of September rather than the 13th. Although this doesn't always hold true, normal practice for the start of a U2 tour leg is to have an off-day between the first and second shows, even if they are in the same city (see San Diego and Toronto on Vertigo's first and third legs).
The opening nights of these tour legs had back-to-back shows:
-Europe 2005
-Europe 2001
-Europe 1997
-North America Fall 1997
-Oz 1993
-North America Fall 1992
-North America Fall 1987
-Europe 1989
-Oz 1989
The only relative certainty is at least 1 day between barcelona and the next show. Likely to be a 2nd concert or another Spanish city.