Hopw long do PayPal customers have to open a dispute in regards to historical transactions?

When is a merchant using PayPal safe from chargebacks for an Ebay item?

45 days from purchase. Details can be found here: pages.ebay.com/help/buy/item-not-re...

If you paid by credit card or if your PayPal account is linked to a credit card you have 60 days to do a charge back with credit card company.