Arriving at Changsha Airport at 11p.m.

Well, don't worry. There still have airport shuttle buses at that time. The Main Railway Station bus line will last until the arrival of the final flight. So you can catch it. The ticket fare is CNY 15.5 per person.
At airport, the ticket counters are located at Gate No.1 and 2, Arrival Hall, T2. Purchase the bus tickets there. Then you can easily find 15 pick-up stations outside the Arrival Hall of T2.