If so, You can fly from Beijing to Xian for one day and then fly back to Beijing. Or you could take night train from Beijing to Xi'an to visit the Terracotta Warriors and Horses(https://www.travelchinaguide.com/attraction/shaanxi/xian/terra_cotta_army/) . One day is OK to visit the Terracotta Warriors . I suggest you to join a one day Xian Terracotta Warriors Tour(https://www.travelchinaguide.com/package/tour-xa03.htm) which would arrange everything OK for you. You could save a lot of time and money.