Sellers like to be paid immediately, and when someone buys an item there is really no truly acceptable reason for delay, not once the person finds out he's won the auction.
However, as a seller cannot file an Unpaid Item case before 4 days, - a buyer can take up to 96 hours. Some sellers will wait up to a week before filing an Unpaid case, but not most. Once the Unpaid process has been initiated, the buyer has a further 4 days to pay and if not, the case is closed, the buyer gets a strike on his record, - and the seller finally gets to relist her item. This is how it works from a seller's perspective:
http://pages.ebay.ca/help/sell/unpaid-items.html
But most important, and what every new buyer needs to know, is just how crucial it is to meet one's financial obligations. It seems no one is taught that at home any more. So have a look at the following link regarding nonpayment and its consequences:
http://pages.ebay.ca/help/buy/questions/unpaid-item.html
Additionally, most sellers block people with 2 or more Unpaid strikes, so getting more than one usually means not using ebay for a year, because strikes last 12 months. Prompt payment is definitely the way to go. 🙂