He's going to destroy it all.
So, Superman instructs the little thieves to go door to door in their neighborhood telling everyone to leave their houses if they don't want to die, literally putting the lives of hundreds of innocent people in the hands of a bunch of wanted criminals. With that out of the way, and having given the people mere minutes to get their valuables out of their homes, Superman gets to work.
Superman, hoping no one will notice that he put his shirt on backward this morning.
Superman starts destroying all the houses, under the logic that the government will then have to build new ones and that this will somehow end all crime. At no point does Superman consult the people who actually live there, or attempt to hide the fact that he's having way too much fun wrecking their homes.
"A long time" meaning when he destroyed a South American village that morning.