I've been flying NW out of LGA for a few months now - this type of thing happens in the NYC area more than you think. There are a lot of weather delays (never experienced 5 1/2 hours but have had some long ones). Here's what has happened to me on more than one occassion.

It had just finished raining and more storms were quickly moving in. Our inbound was delayed for 2+ hours in a holding pattern. When it landed, the GA told us in no nonsense terms, board only when we call your row and board quickly, if we don't get you pushed back from the gate soon, the crew will time out for the night. After the plane door was closed the pilot came on and told us that we were going to push back but it didn't look good. We HAD to get in line for takeoff because they only let 30 planes in line. BUT we were going to have to sit on the plane because they had just shut down EWR and the rain was moving in quickly, after that ATC would start releasing planes but who knows how long before we could take off. The good news was, a lot of other inbound planes had to land elsewhere for refuel, but he didn't and that it sounded like it helped the crew not time out. We sat for 2 hours and then were released, my friend on a United plane at the same time waited for 3+ hours to take off. No riots on my plane, the pilot let us use phones and get up and "move about the cabin" - just be ready to get back in your seats quickly if/when we get released and it was a packed 757 with every seat taken (or so the GA said).

It's not just a CO thing for this type of delay, it happens on NW too. I have lots more NW delay stories out of the NYC area if you think NW is better at getting out of there in that type of situation (I'm a NW plat by the way and I really like them, for the most part).