Here's the thing... You want to try and buy a UY that is 1 month ahead of your preferred travel time. For example you buy a Jan UY if your preferred month to travel is Dec., so as soon as you get your points, you can start booking in the 11 month window. Other reasons why you want to own a UY that is 12 out form when you " usually" travel is ...
1) If you book as early as possible, then if you need to cancel, it is much safer to cancel farther out from your travel date without any penalty.
2) Also, you have more time to decide if you are going to bank your points without facing penalties.
Hope that makes sense. IMO it would not be beneficial to buy Dec points unless you plan on traveling in Nov. If you think you are most likely to travel at Spring Break or early summer because of school, then pick a UY around April- June.