Generally with Visa and Mastercard, you have 6 months to file a dispute WITH the US and 12 months to file an overseas dispute.

I know this b/c of a fraudulent sporran purchased by a guy in Russia (who we shipped it to) who used a credit card of a man in Japan. The sporran was purchased and shipped in January and the 'chargeback' happened in September, a full 9 months later. I got stuck for the $500 'head on sporran'.