If the item is not as described, I open a case first and then later I contact the seller (irregardless of the fact that eBay states that you have to contact the seller first). So to answer your question; "0" days and on a $500+ item it's probably less then that
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Good luck! By the way, when you are filling out the eBay questionnaire just state that the item was not as described and don't go into too much detail (anything you say could be used against you if the seller does not accept returns................book-'em-Danno!).
Lovely Day...