Old thread but I would avoid the train and just fly. Last time I flew out in the am, did the tour and flew back to Beijing that night. Easy peasy and a short flight. Yes the airport is not in the city but an arranged tour would pick you up and drop you off.

Honestly, the warriors are very cool but you would not spend hours there. I added a quick city tour and some lunch and did not feel I was hurried or missed anything.