My friend and I found a great fireworks spot 15 minutes ahead of the show 2 Sundays ago. The crowds are not so bad that you need to scope out spots that early for either fireworks or the second show of the parade. As we left the parks around 10:40 one night (with a 10:45 parade time), there were numerous spots along Main Street that we could have stopped and stood or sat to watch the next parade.
I am going tonight with my kids to catch the first parade because last Saturday was WAY too packed to get a decent spot for it so we just left. Our plan tonight, since it's a weeknight/school night is to start looking for a spot around 8:15. I'd like to find a spot near Small World so we can hightail it out as soon as the last float passes by (it starts at Small World for the first parade, and Town Square for the second).
However, my general preference is to watch from near the train station or the Emporium. I like watching the floats make the turn. You should be fine looking for a spot 30 minutes out. Be willing to split up, though.