Since JFK has entered full meltdown mode in the last couple months I have been two-hours-extended twice. But those were the first times since I have been here. None of them were the companies fault. In fact, the second time we actually called DX and they managed to move up our EDCT time. Now I am rambling.
In the end, Endeavor is pretty good about this. On the 900 at least, most of our trips that touch NYC are build to withstand some stuff going wrong.