Like others, this past year we booked at the 90 days mark. IMO, our experience wasn't great. While the show was wonderful, we were seated 45 late for dinner (after our ressi time) and it took us 45 minutes to get our food. We ate in Paris and the food was so so. Since the weather was marginal there were seats available to the general public.
Since I have seen it once, next time we will wing it and try for a spot without reservations or stand out side and watch.
It is a must see at least once.
Good Luck,
Gail