How early will depend on how many people. If you're alone you can squeeze in somewhere an hour before and not have to stand too long to wait. I watched it from the far end of Main St. Once the parade ends everyone can go into the street and if you move quickly you can be mid-Main St to see both the castle and the buildings on Main St. I haven't done the hub for the parade or Matterhorn view for the fireworks yet, so can't advise. If you have 2 or more people who want to see the parade together then I'd advise to stake a spot earlier.