The "standard" is that it can take up to two hours, though it naturally varies depending on how many cars you have that day, and of course even with a full train the cars off early can be on their way. Few people will therefore ever have to wait the full time to unload everything; the unlucky party whose vehicle is last off being the exception. Most people will probably be on their way inside of an hour, but again, allow two.
It's not a completely random process, though it may appear so (and thats the easiest explanation). The vehicles have to be taken off in the same order they were loaded into individual auto carrier cars, but the first carriers to be loaded could be the last unloaded, or something in between. You have little way of knowing where in the train your vehicle is, whethor it ended up at the front or rear of a given auto rack car (or cut of cars), so really it may as well be completely random.
