There is really no reason not to pay right away, or the instant the buyer knows he's won the auction. However, a seller cannot file an Unpaid Item case for 4 days. That certainly allows lots of time to pay. Once the Unpaid case is open, the buyer then has a further 4 days to pay and if nothing, the seller closes the case, gets her selling fees back and relists the item. No one leaves feedback.
Is that for the epiphone? It's been 4 days now. Have you sent a friendly reminder note to the buyer? What most sellers do is send a kind reminder on day 3 (sometimes buyers do get busy and forget), and if no response, they open an Unpaid Item case at the end of day 4 (hour 96 is the earliest possible). The following link will tell you how to do that:
http://pages.ebay.ca/help/sell/unpaid-items.html