You can start an Unpaid Item Dispute after 4 days (96 hours).
I usually send a polite note on Day Three asking if the buyer needs help with Paypal. Just a little nudge.
Most buyers then send money, an apology and positive feedback.
The rest disappear. I open the UID , close it after another 4 days, relist and add the buyer to my Blocked Bidder List.
He then cannot leave feedback , has a UID Strike that will make it harder to bid on eBay, and I get my selling FVF back.
Check your Seller Preferences for automatic Blocks against unwanted bidders.