Wouldn’t this depend on the terms of your contract? Work contracts usually have a start date (and end date if it’s not a permanent placement).
If the start date precedes your interview date, then it’s safe to assume it’s not valid because you haven’t started your job (you’ve abandoned your post). If your start date succeeds your interview date, and the time it will take you to travel to the US (assuming your aren’t living there already), then it should be valid.
Unless your contract states that you’ll have a job waiting for you, however long it takes to legally get to the US, then I wouldn’t bother taking it to the interview. One exception is asking your prospective employer to either change the terms of your contract, or furnish a letter stating that your job will be waiting for you given that you get the visa.