While there is not theoretical maximum, the seller can open an Unpaid Item Dispute if the buyer takes too long.
Have you sent an invoice to your customer with the correct shipping? Sorry to sound so silly, but eBay does not always send invoices automatically.
If you have, wait for three days, then send a polite reminder. I usually ask if the customer needs help with his Paypal account. I probably can't do anything, but it serves as a little nudge.
On Day Four, open an Unpaid Item Dispute. This will either push your customer into paying or will close the transaction, refund your selling fees, give the deadbeat a Strike which will make it more difficult for him to bid on eBay in future, and block him from leaving feedback.
Not every sale is worth having. Those from Nigeria for example.
Also, go to your Seller Preferences and set up automatic Blocks against bidders with Unpaid Item Strikes, bidders without active Paypal accounts, and bidders from countries you do not want to ship to. (At this point in your selling, I would not advise shipping outside North America.)
