10 days from the date of posting the shipping information, you are supposed to receive the item. If you don't confirm receipt of the item in 10 days, you get an option to raise a dispute saying that you have not received it. This is of course assuming you have not received it. At this point of time, there is an automatic 'grace' period that kicks in - irrespective of whether you open a dispute or not - of 5 days. So in all, 15 days from the date of posting of shipping info is when you are supposed to receive / confirm receipt. If you have not received the item in this duration, make sure you mark as not received, else you will lose the ability to do that and eBay auto treats the item as received. You can still open a dispute, but it would be late by then as eBay would have started processing the payment to the seller.