I think it really depends on the parade. For example, if Spectro is only shown once during the night, people will stake out about an hour before the parade (however, I have a spot where I have never had to arrive more then 25-30 minutes before). But if there is a night with 2 Spectros, go to the 2nd one. It is almost always a lot less crowded. The day parade is usually never too bad. Again, I usually get there (same spot) no more then 20 minutes prior. At MGM, that parade is always easy to find a spot for, so don't worry about that one. And at AK, it's usually pretty easy to find a spot. It ends where it starts, so if you wait about 20 minutes after the parade begins, you can go to Africa by the Safari ride and have almost no one there as you catch the parade returning to the end.