Most of it depends on whether you are "drive in" or "fly in" destination. We are a drive-in destination, so take these figures with a grain of salt:
Our shoulder seasons (Spring and Fall) always book late - often just 2-3 weeks in advance.
Summer (mid-June to Labor Day) books about 1-2 months in advance.
Our Christmas/New years usually book 3-4 months in advance, and ski-weeks, especially 3-day weekends are usually booked 5-6 months in advance.
I would imagine Fly-In locations book much farther in advance, so if you are just starting and the next 2 months are empty, it may be too late to get them filled. But don't let it scare you off - they will likely fill next year when people have had more time to plan their vacations to use those weeks.
I should add that even through the high seasons we don't get 100% booked until very late in the game - especially in the winter. Last year's mild winter kept people guessing and hoping that the weather would turn colder as they waited longer and longer. When it was all said and done, we ended up renting every week, but for a few of them it was only 2 weeks in advance. I suspect that unless we get some good, cold weather this November and it sticks around solidly through January, it will be a slow-to-fill winter again.