Short answer Sept or Oct.
You want to be able to give yourself the longest possible time to "recoup" your points if you need to cancel.
An self example was one last year, where I had to use my points from my April UY for our March trip. We usually use our Feb points, but things happen. And things did happen, snow storm in Buffalo, not as bad as last week, but enough to shut the airport. Out of our 7 nights we lost 3. Those points only had enough time to now be used in the next 45 days, not going to happen.
Thankfully we didn't lose them, and a great CM was able to get them banked for me due to the weather, and we used them in Sept.
So yes UY does make a difference, and habits do change.