AlmightyKfish
This Is No Longer A City.
If it's destroy the planet, surely Thanos could do that instantly? If he teleports in undetected, with instant knowledge he wants to destroy the planet he's landed on, it's within his own power to just blow it up.
That being said, he's unlikely to be able to conquer the Earth, Pre-Nu52 DC earth was stacked as hell- far more herald level and beyond beings in the general hero populus, as well as a huge number of super scientists and strategists.
I mean, with a month Thanos can probably do a lot, but not enough imo, considering he has to assess and deal with so many new variables- understanding DC's alien races on Earth, the speed force, GL corps, DC's magic...
He just isn't going to physically have enough time to prepare for every eventuality, and his opposition is too varied to be able to counter.