If you have not paid, after 4 days (96 hours) the seller can open an Unpaid Item Strike.
You can communicate with him through the dispute, but if he doesn't accept your excuses, you will get a Strike that will make it more difficult to bid on eBay.
If you have paid, your payment will be held until it clears your bank (unless you backed your PP account with a credit card) which takes about 10 days. After that the seller has up to 7 days to get the item mailed.
Some new sellers, and sellers with poor reputations, further have your cleared payment held for up to 21 days. This is against their good performance and is a Buyer Protection policy. Occasionally a seller will get his panties in a bunch about this and try to cancel the sale.