This is not "days on market" in aggregate though. This is the percentage of the current listings, which are older than a month. Imagine a very hot market, where almost anything gets snatched the same day. Any listings in such a market that will remain for longer than a day are some overpriced hovels, which nobody wants to buy for any price. So the percentage of the listings that had been "sitting for longer than a month" can be anything in there, depending on how many people wanted to put up their hovel at ridiculous price and the "days on market" can be under 2 days.