I suggest you take train to Xian. I know there are several trains from Shanghai can reach Xian in early morning. Then you can get tourist bus 306 (游5)at the east square of the railway station. The destination of the bus route is the terra cotta warriors. you can also pay a visit to HuaqingChi (Hot Spring)not far away from the terra cotta. You journey can be ended in the afternoon. Then you can get back to the city proper. It your time back is not too tight, you can get around the Bell Tower, Drum Tower or the Muslim Street. Rent a taxi for one day trip to the terra cotta is a little more than 200 yuan. You can also consider that.