The arenas won't just block out their schedules for 2 weeks for U2 residencies. On the days that U2 don't play, the stage will be loaded out and other events will happen in the arena. This is a fairly common practice. It's why U2's shows in Chicago 2005 were May 7, 9, 10, 12. Or why Boston was May 24,26 and 28. Or why the 2 Philadelphia shows were a week apart. The arenas have to schedule around NBA or NHL games, and things like playoff games are at this point unknown.
Last year the Rolling Stones announced a show for LA Staples Center, but didn't know which date it would be on, depending on playoff schedules. I think tickets were even sold with the understanding that the show might be on Friday or Saturday, for example.
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