The actual parade lasts around 15-20 minutes. Thats if you are standing in one spot throughout. But - it stops twice in the parade route, so from the start of the parade route to the end of the parade route, its nearer 35-40 minutes (we dashed down the arcade on one of our trips at 4.30 and caught the last half-dozen floats right at the end of the parade route ).
We watched the parade at the start from near Belle Notte and it was about 15 minutes
As Elaine says if you were to walk towards the exit after the last float had passed you it would still be running
Yes, you should bag a spot and stay there - to see the whole parade as it passes you. And then you'll probably want to see it the next day, and the next etc etc (you get the picture ?)
As already said you find a spot and watch the parade pass but twice during the parade the floats stop and characters get off to dance etc. If you are lucky enough to be standing near one of these stops you can watch them and often get to shake hands with some of the characters. There is a good page on DLRP magic where the parade is described and the stops are highlighted