It seems you can call and start the award booking process and wait to finalize the transaction until days before flight date, if that's how you roll. (viewfromthewing.boardingarea.com)
-- Members may request missing points from flights up to 90 days from flight date. (insideflyer.com)
Provide your departure airport and destination, plus your preferred flight dates, then compare prices across several airlines. (nerdwallet.com)