I'd be interested in seeing how the time in previous games breaks down. I sincerely doubt that there's that much difference between chatting to folks in earlier games, walking from A to B (Just because you could do so in a more squiggly line doesn't change what you were really doing), and fighting.
In any event, GamesRadar have made me feel a good bit better about FFXIII. Their review addresses most of my concerns and points out that, well, I love FFX to death and that was linear as hell.