It depends on what your contract says. If the down payment was due when you took the car, as it usually is, you have no days. It's due now.
Legal disclaimer: John Bonica is licensed to practice law only in Texas. His response is not legal advice and does not create an attorney/client relationship. The response is only intended to provide general information. The question may not include significant and important facts that would change the response. You should confer with a local attorney for competent legal advice.
Typically, there is no bank error in your favor. If the dealer requests the money, you should pay immediately or the dealer could demand that you return the car. Not paying the down payment is a breach of contract. A buyer cannot rely on a seller's omission to escape paying what is owed under a contract.
You can sleep much better, and earn some credibility points by paying the down payment right now before the dealer realizes the mistake.