Longest, hottest one was the Coca-Cola 100th Anniversary Parade in Atlanta in 1986. It must have been three miles, with all the glass buildings reflecting the heat.
For contrast, most parades are under one mile.
I just looked it up. The Macy's Parade is two and a half miles, but not in Atlanta summer heat.
I was in the bicentennial Disney parade at Disney World (when it was still truly Disney). My sister SHOULD have been there as she was the star lead majorette, but she quit just before this. She was in a lot of local parades (I was just little, and did not do much), mostly summer.
As it was, people were passing out for the Disney parade. I remember mostly just being in a holding shelter until our time was up, and hearing about the teen girls dropping from the heat.
Hey! I might have seen you there! I was in that parade, too, with our high school band from Marietta, Georgia. Can’t honestly say I remember much about it, though. Kool and the Gang and a few other famous acts?