dont have money to fix catalytic converter.. how detrimental is it to wait a month or two to fix?

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What year/make/model are we talking about? I agree with the comments about the 02 sensor. It all depends on how it was diagnosed. I think it's way more common for an 02 sensor to fail than the cat itself.

And you could remove it, depending on emission controls where you are. They call it a "cat delete".