At what point can you no longer exit Kefka's Tower and return to the map?

I want to exit and level after I get as many items/espers as possible.

My cousin, way back in the day, had everything such as Crusader etc.. and was on the world map but that was 10 years ago.

I haven't gone into the tower yet other than doing a moogle-charm raid.

Can I warp out at any point?