No E+ if Traveling on a US Ticket?

So we're on US award tickets with legs on UA, NH, and NZ. For the UA sector where we're stuck in Y, my wife and I (both 1Ks) can't get seats in E+ for free. UA tells us there's nothing they can do until the day of departure at the airport.

Is this correct? Any workarounds? If day of departure only, how far in advance of the flight can we address this, since I'll be at the airport about 12 hours prior? Will an SDC request also have to wait until that time?

Thanks......