We were running late (though Were actually there for 6.30) and only just got seated before the show started.
The staff seemed to almost struggle to seat us (like the seat bookings weren't pre-allocated), and food service was well underway.
I think it simply boils down to it taking X amount of time to get so many people in and seated etc - so be there at a reasonable time and you'll no doubt get in easily and get good seats.
of course, you probably missed a large part of the main parade in the park though! I'd say seeing at least some parade, then making a dash to get there for 6 is a decent balance.