I tend to consider anything over a couple of hours as fairly long - I used to do Bristol-Edinburgh fairly frequently (just over two hours), and since have done several London-Switzeland trips. As has alrady been pointed out though, these aren't 'cross country' in the sense of qualifying for a rating
I used to do the drive to Edinburgh in one hit on the road (about 5 to 6 hours), where the speed was regulated by the range of the car (much over the legal limit would require a fuel stop), and not sure if its to do with the flying or age, but find that a pee about half an hour before departure, followed by another immediately before gets around the bladder problem (your mileage may vary
) I have yet to declare a pan due to to a hydraulic system overpressure warning, but it's been mighty close a few times