You'll be making a full day of it regardless, since it will take you at least a few hours to play. The mountain recently cut back its tram service so that the last car leaves high camp at 5pm (they had been pushing it to 9pm). After that, you'd need to walk down the mountain which takes about an hour. The first tram up leaves at 10:45 am, so it is unlikely that you'd get two rounds in at this point.
Regardless, I'd wait until next year, after they pour the concrete tees and get the full course signage up.