Your anniversary points will post on the next statement after your anniversary had taken place. What's important here is to realize when your statement end date is. If the next statement ends in November, obviously that won't work. Changing your statement end date to the 20th like you suggested should work. While you can't change the statement end date directly, you can change it indirectly by changing your payment due date. The payment due date is usually 3 days before the previous statement end date. So in this case, changing your payment due date to the 17th of the month would change your statement end date to the 20th.

I would also caution you about waiting too long to change this. Sometimes changing a payment due date will result in a longer billing cycle. For example, if you were to wait till late September to do this, it's possible you're next statement end date would be in November and would defeat the whole purpose of doing this to begin with.