Maybe I've just been lucky, but ........
every Memorial Day Weekend between 1997 and 2002 I have been arriving as early as 6AM and late as 7:15AM and never had a problem at the Adirondak Loj. But take that with a grain of salt, the previous posters live closer than I do and have more experience in that area. Plus, I wouldn't be surprised if the number of people increase every year, so getting there before I did is probably good advice.
Just my two cents ....