How long are such NDAs legally enforceable? If I sign the NDA and work at Apple for month am I prohibited from ever discussing ideas developed under NDA during

How long are such NDAs legally enforceable? If I sign the NDA and work at Apple for month am I prohibited from ever discussing ideas developed under NDA during that month? Has there been any meaningful test of this in court? What if Apple releases a product that incorporates aspects of the ideas but not all of them? Is Bret still unable to speak of his work (even if he limits it to the aspects publicly disclosed by Apple)?