Actually, the amount of time you choose for Ifrit's Cave is irrelevant, it's how much time is left once you've completed it. The longer the difference is, the less points you get. The trick to getting a full score of 100 on this little bit is to pick any of the time limits (40 minutes is the safest really), and defeat Ifrit at your own pace. Once it gets to the experience/ability points/items won screen, put down your controller and walk away. You cannot get a game over if the timer (which is now invisible) hits 00:00 at this point, but you do get accredited the full score. I think all of that's covered in the FAQ Endless. linked to (btw, you're not supposed to direct-link to the FAQs on GameFAQs, they specifically ask you not to)