I have booked three roundtrips on United using miles for later in 2015. One trip was booked 337 days in advance of travel, while the others 9 to 10 months in advance.

While I didn't always receive my first choice of departures, the available choices were adequate for our needs.

Similarly, I also booked three roundtrips on Southwest, admittedly an easier task, and one on Alaska.

Fairly good results.