It will take 3 to 6 months to determine that a new hire is incompetent, especially if you're required to document their incompetence before firing them.
I've never had a job without a probation period where you can let someone go without cause within the first 90 days with nothing more than two weeks pay in lieu of notice. It definitely doesn't take 6 months to identify someone who only got their job because they used AI in the interview.