For a frequently bought/sold item like these speakers, you can get a pretty good sense of “how long?” by visiting HiFiShark, entering make and model, and tabbing over to “Sold/Expired” results. That will provide you with your best collection of comparables and include info on where sold, for how much, and in how long.
This is also a good method to use on the buy side when the seller is asking 18 million dollars and you’re able to say, “no, the last dozen have sold for an average of $227. The other one listed for 18 million dollars has been for sale for a decade.”
P.S. Why so many daft responses in this thread? This is actually a legit question/issue if you actually give it some thought.