You have more than ten days, this is what eBay says,
'Item not as described
A buyer must request a return no later than 30 days after the actual (or latest estimated) delivery date, or, if the seller’s return window is longer, within the return window.The seller has 8 days from the request to respond to the buyer or offer a solution. If the seller does not respond or offer a solution, the buyer can ask us to step in and help.The buyer must ship the item back to the seller within 14 days from when the buyer starts the return. If the seller offers a refund and doesn’t send it within 6 business days of the item’s delivery to the seller, the buyer can ask us to step in and help for a period of 10 business days after the refund deadline has passed. If the buyer doesn’t ask us to step in and help within 30 days of starting a request for a return (or the timelines described if a refund or replacement isn’t received), the request closes automatically.'