Being a freelance pianist, I'm never sure when the next big gig is going to be. I'd love to jump on an F award 330 days out but the opportunity cost could be in the hundreds or thousands if I get offered something lucrative with only a month's notice.
So I generally plan vaguely a few months ahead for a big annual trip of a month. I'll put stuff on hold but I don't lock in until I absolutely have to (thanks, KE award holds!). I don't firm things up until 4 to 6 weeks out.
Occasionally I have two stretches of lots of work planned in advance and can use those to book-end a month off when I don't mind giving up a few odd dates, but that's rare.
Seth