Unless you want Anna and Elsa and perhaps if you have set days for 7DMT.
I am 33 days out. I booked at 60 but yesterday I went in and changed a few days and had no trouble - even with 7DMT. Choice of times throughout the day too.
Oh and we are there over July 4th. September should be a piece of cake
I can confirm that so far 60 days out exactly is really only required for Anna and Elsa. I booked aprox 45 days out for the week preceeding Independence Day. And like the poster above me have switched some things as recently as today without a problem.