The first time we wen to Fantasmic, during one of the slowest times of the year - the first week of December, there was only one show and only standing room available at the back. I believe we arrived at the show about 45 min before showtime. We stood there for a while and then decided to leave a come back later in the trip but come back much, much earlier to get a good seat. When we came back a few days later, we arrived 2 hours ahead of time to claim our seats.
As long as the Fantasmic dinner package is available, this is the way I will see Fantasmic no matter what time of year it is. I don't want to burn valuable park time sitting on bleachers.
You have to make a priority seating arrangement for the package and guarantee it with a credit card. Call 407-WDW-DINE. You can cancel up to 48 hours in advance with no penalty. If you are a no-show for your priority seating, your card will be charged $10 per person.
The package is fixed price with a different price for each restaurant. The restaurant choices (in order of most expensive to least expensive) are the Brown Derby, Mama Melorse's, and Hollywood & Vine.