Use a morning for the Terracotta Warriors and keep the return afternoon loose. On the other day, let the city wall, neighbourhood food, and museums decide the pace.
Treat the museum visit as a half-day
Transport, queues, and the scale of the site add up. A rushed visit often misses the context that makes the figures meaningful.
Read the city after dark
Xi'an changes in the evening. A walk around the wall or through older food streets is usually more memorable when it is not reduced to a checklist.