Mostly the first parade is the busiest while the 2nd one is the least busiest.
People would wait as long as 1+ hour for a spot for the parade on MS. MS is one of the places where most of the guests watch the parade. You could get a front row spot on the parade route at MS with about 30 minutes until the show. The place which is the least crowded spot for the parade is around IASW. I have seen people get a good spot 10 minutes until the parade.