I don’t recall this, but according to Investopedia: “No more than one month had elapsed before the Dow Jones, the Nasdaq and the S&P had regained its pre-9/11 price levels.”
https://www.investopedia.com/financial-edge/0911/how-september-11-affected-the-u.s.-stock-market.aspx
True however we did not SHUT DOWN the entire economy over 9/11!,