How long can a creditor hold vehicle after money has been paid on a repo?

That's not enough information. First, we're not lawyers, you'll need to explain things to a lawyer or go to the bank to see what's going on. Second, it all depends on what the original loan documents said. Once you're past due or in any way violate the terms of the agreement, they can take the vehicle and sell it. If you pay off the loan after that, it's possibly just a bonus for them. Remember that once you have defaulted on the loan, all bets are off and you don't have any real protection under the law.