I finished the main story in 65 hours and got the platinum in 97 hours. I took my sweet time during story so YMMV. --- There is a board for RPG, you know: http://www.gamefaqs.com/boards/220-rpgs-everything-else
I took my time, collected all the familiars, screwed around and really took a very slow pace trying to really enjoy and explore everything. All side quests, all items, and did all the alchemy that was possible plus I wasted a chunk of time in the casino playing a card game I liked. I also maxed out a number of familiars.
I squeezed out every possible thing to do and had around 100 to 120 hours in it.
But I could easily see someone playing for 30 hours and being done. The game is super easy and at end game most of the familiars I was using were ones I got early on and never really went out of my way to get.
Unless you hate the game and quit I would put an average playthrough at maybe 50 hours. Less for people who go straight through the story, more for people who collect familiars for completion purposes. --- PSN ID: sled_dogs76 60" Pioneer Kuro Elite PRO151FD, Yamaha RX-V3900 A/V Receiver, Oppo DV983-H player. Coming soon: 2 Seaton Submersives from Mark Seaton