It depends on the state that you are located in, the contract that you signed and the lender that you have a loan with. I am a recovery agent in Ohio and some lenders don't place a car up for repossession until it is 6 months past due while others will place an order for repossession after the debtor is 3 days late....depending on the contract that was signed.
Answer
Legally, the moment you default on your loan (1 day late). A lender will usually attempt to see whats going on. If its a sub prime loan they will be quick to try to collect. Work something out if you can, even though you are late lenders should be courteous. Be nice and work something out and keep commitments, even if its for a partial payment.