Does anyone know if you can get advanced seat assignments on an AV award booking on AV in economy, or do you have to wait until 24 hours before departure to get seats?

I am looking to book a one-way award ticket on an AV flight from JFK to CTG nonstop in Economy using Lifemiles. I am travelling with a young child and would like the certainty of adjacent seats ahead of time, but I cannot find any details on the website about whether I can get an advanced seat assignment, or if I have to wait until 24 hours before the flight to get seats. Unfortunately, 2 calls to Lifemiles ended up with very long hold times and 2 different answers. I would like to know this before transferring miles to AV (and cannot start a dummy booking to check without sufficient miles already being in the account).

There are two prices offered for this flight in economy -- "Economy on Sale" for 17.5k miles, and "Economy" for 23k. Happy to pay the 23k miles if that's what it takes.

Thanks for any help