I can recall a 7 or 8 hour delay about 12 years ago. Flying ORD to DFW on the Wednesday before Thanksgiving and Chicago got hit with its first big snowstorm of the year. Fortunately, I was flying AA on an internationally configured plane that was being repositioned to Dallas, and had snagged an upgrade to first. So I spent 10+ hours in one of the "coffin" seats on a ticket that cost me a couple hundred bucks. (If one I'd earned the miles I would have earned on a flight that long.) As I understood it from the FAs, we pushed back from the gate shortly before the crew went illegal, but they were Dallas-based and motivated to get home for Thanksgiving, so they were as eager as we were to make the flight.

All in all, I think we boarded at about 5 pm and landed close to 3 am. Clearly, this was before the tarmac delay rules went into effect. (And they may have given passengers the option of offloading while we were still at the gate. I was comfy in my seat, so didn't take them up on that.)