Uhh. 30 hours, give or take. I just played through the game, got Yuna's Ultimate Weapon, got the hidden aeons, and that was it. 300+ DORKS. (J.k.)

If you fight in the Omega Ruins you can get some Lvl. 3 and Lvl. 4 Key Spheres. There's also one monster (Chimera or Chimera Brain I believe..) you can capture and fight in the Calm Lands and if you bribe him (I don't know exactly how much Gil.. but you can look it up somewhere.), he gives you 2 Lvl. 4 Key Speres. Hope that helps.