I did this the other day, but in reverse. I went from Gridania to Limsa Lominsa. It took about 35 minutes for the whole journey. Just follow the path, but if you're more daring you can take shortcuts; though mind you there are some very dangerous mobs out there. Rock Piests, Ants for sure, Spiders will definitely eat you up like candy.
It's not who we are, but what we do that define us. - Batman Begins