When we bought our BWV points, we were given the choice of February or June. Not sure why they were our only selection....
I didn't think too much about it at the time, except that it was more likely that we'd be doing summer trips (with kids), and when we bought, our kids finished up their year in June. So we have a whole year to figure out how to spend them. Here are the lessons I've learned so far...
Lesson 1: One month prior to your normal vacation season.
If you vacation in the summer, take May or June. That way, you can freely make/change reservations throughout your "season" without any concerns, and have a whole year to do something with the points.
Lesson 2: Things change.
How you vacationed pre-
DVC is not likely to be the same, post-DVC. You'll likely vacation more

. Also, I'm fully expecting that within the next 10 years our vacation pattern will change again, as the kids leave home... them grandkids will come along, changing our plans yet again.
Lesson 3: The point system is very flexible.
I think about vacation plans, every weekend.

You'll discover in most cases, banking and borrowing will give you enough flexibility where any use year will work.