You can check your baggage yourself at the railway station 3 days before taking the train. It will take 13 to 18.5 hours by train from Chengdu to Xian and all the trains are overnight ones. So, to see the scenery from the train, you can take a train at noon, for example: T8, 11:40-00:24; K880, 12:25-05:33; K166, 13:15-05:16.