We have used the train twice, both times it was around 10 to 12 hour trip, with one changeover. But it was a great way to travel if you have the time. Nice and relaxing, see the countryside, less worry about your luggage.
Take your own water and snacks.
With the "hub" system and all the stopovers for some of these airlines, it is getting to be almost as much time unless you are flying out of and into a major centre.