I have been selecting the Immediate Payment Required when listing items lately. What is the time limit on this?
Immediate payment is a listing-by-listing option, and it stays with the listing for as long as the listing exists. It does not matter if you have been choosing it "when listing lately", it matters if you chose it for the exact listing your buyer purchased.
I currently have the box checked about limiting buyers who didn't pay etc. but I imagine that went out the window after one year, right?
Where is this box you are referring to? Are you talking about Buyer Requirements? If so, the box that says "Block buyers who caused X cancellations of unpaid order within Y month(s)" has the answer is in the description of the option itself. It will do exactly what it says - block any buyer who has caused at least X non-payment cancellations in the past Y months. Nothing "went out the window". But when setting that option, you need to choose the option to apply to active listings, otherwise it will only apply to future listings.
I'm also guessing that sellers didn't report the non-payments in the past and that's why they still have an open account.
eBay doesn't close buyer accounts for non-payment, whether or not they are reported. eBay counts their nonpayment cancellations, and as discussed above they allow sellers to block any buyer who has caused at least X non-payment cancellations in the past Y months if the seller chooses to.
I was tempted to send them a message acknowledging that I'm aware of the non-payments, but just decided to wait it out
That would serve no purpose except to perhaps provoke them to retaliate. The buyer knows he won, and eBay reminds him to pay. He will either pay or he won't, and every minute you spend agonizing about it is a minute you have lost forever.
