If you want the front row seats, get over to the line-up by Harbor House (near Haunted Mansion) before or as close to 8:00 as possible. If you aren't as picky, 8:30ish will be fine for a 9:00 show.
We were there only about 8 weeks after the new Fantasmic opening last summer (on the first night local APs were unblocked) and still found center seating in the back row (my preference for taking pictures because you don't have the rail in the way and don't annoy people behind you) around 8:40.
PHXscuba