I think you can get spots a half hour before parade time. But if it's hot out and you want shade, you'll need to be there sooner. I got there earlier than that, but was very particular about where I wanted to photograph the parade from. I was on a porch in front of the shops, in a place where the rope would come right in front of us, leaving no room for someone to squeeze in last minute. Here's the view:
IMG_7137 by
mom2rtk, on Flickr