Yep, timing is important. If it's before the Festival of Fantasy Parade in the afternoon, the train station is a great spot. The fastpass area isn't a bad place to watch, but it is not good for filming, because people are permitted to walk back and forth in front of you (between you and the kids) up until the band is almost on top of you.
If it's the evening parade, before MSEP, be aware the lighting is tricky. The best spot (since they are coming UP Main Street toward the castle instead of the other way), is at the edge of the Hub, looking toward the train station. If you don't get there before people have saved the spots, I find that if I politely explain that I am only watching the band, they don't have a problem letting me get to the edge to get some great shots. With the understanding that I will leave or move to the back after the band passes, of course!
I am a tour director for high school bands and choirs, so I go 7-8 times a year. Let me know if you have any other questions about a band trip.