I've used miles four years in a row for First Class to Australia for 2 people. It didn't work out last year, because I needed to stop over in New Zealand (so I used my AAdvantage miles on Qantas and Air Tahiti Nui for 165,000 miles --United is just 120,000, one of the best deals in air miles).

I booked last month and have exactly the flights I want for next winner. 330 or so days ahead works well or alternatively, a month or so ahead also seems to work.

Best of luck.