i booked our apartments for our upcoming October trip just under a year in advance. the air we got a couple weeks ago, but it could have been done closer to the end of the summer i suppose. this goes back to another thread onhere.
it also depends on how far in advance the establishment will take reservations.
my opinion: anything more than a year out is excessive for just a vacation. with a May trip of next year, you're fine to make 'em any time now.
Lately it occurs to me what a long, strange trip its been