When can I return to Besaid

All -

I'm a rookie at this, but the Besaid Destruction Sphere appears to be one that I'm missing in order to lock up Anima - I know, how much easier can it get - but I blew through it not realizing what I would miss until a buddy showed me ANIMA.

I'm on the Airship now and I try to return to Besaid, but they will not let me in the temple! Is my shot at Anima screwed up now, or will this be time or event trigger released? If it's event released, what do I need to do?

Any help would be great!

I think it's when the 'Inside Sin' location is avaliable on the airship (In other words, the time in the game when only the final dungeon and bosses are left.). If you have the PAL version, you're also gonna have to beat Dark Valefor to get to the temple. Good Luck.