Hi Michelle!
Congratulations on your September Walt Disney World vacation!
Nighttime shows throughout the parks are usually published 3 months ahead online on such Disney Fan sites as allearsnet.com.
However, with the Fantastmic! Dining package, since it's a dining reservation, you can find out the nights it's showing by doing a search for available reservations under the Fantasmic! Dining package online on Disney Dining or by calling a Disney Dining Cast Member to assist you at (407) WDW-DINE.
If you're staying at a Walt Disney World Resort, you'll be able to begin your
online dining reservations on Sunday March 25th and reserve for the duration of your stay. If staying off-site, you'll be able to reserve each date of your stay as it hits the 180 day mark.
I'd suggest that you call in on Sunday morning and have a Cast Member assist you in selecting the evening of your vacation and dining location that works best for you! I highly recommend Mama Melrose's Ristorante Italiano for your package. Be sure to indulge in a Spaghetti & Meatball Cupcake!
Wishing you a Magical time at Walt Disney World Michelle!
Kirsten