7 days to notify the seller you don't want the goods and will be returning them - you must return them as soon as is practicable.
Distance Selling Regs apply to business sellers on eBay if the listing was BIN or it was a 2nd Chance Offer.
Refer your seller to this:
Distance Selling Regulations
The Consumer Protection (Distance Selling) Regulations 2000 generally apply to sales to consumers made by sellers acting in the course of a business, which have been made at a distance. In other words, where there's no face-to-face contact between the seller and the consumer before the contract is made. The Distance Selling Regulations apply to items purchased via Buy It Now listings and Second Chance Offers on eBay.co.uk. However, they don't apply to auction format listings on eBay.co.uk.
The Regulations also provide a period of seven working days after the date of receipt within which the consumer can cancel the contract (often referred to as the "cooling off" period) and get their money back, including the original postage and packing charges. The consumer can be asked to return the goods at their own expense, but only if the seller informed them of this requirement before the contract was made (otherwise, the seller is responsible for collecting the goods). If a business seller has not provided the information required under the Distance Selling Regulations (as discussed above), the buyer will have up to 3 months to cancel the contract and get their money back.
http://pages.ebay.co.uk/consumer-rights/consum er-rights.html