I will arrive at Xi´an at 11:24 am from Beijing.

Yes, it is possible. You can first purchase the ticket of Terracotta Warriors at the service point of North Railway Station, located at the south of the entrance of subway line 2 on the negative layer of North Railway Station, by virtue of your high speed train ticket on that day. Then, use the attraction ticket to exchange the bus card to take the tourism bus freely. The departing time is from 08:00 to 16:00 every day. The bus leaves every hour and runs in both directions at the same time.

But the bus usually is opened on holidays or tourism peak seasons. So you can also consider the second way: take the Bus No.266 to Xian Railway Station and then take the Bus No. 306 at the square of the station, with ticket price of about CNY7 and duration of about half an hour. There will be a little crowded at your arrival time because September is a hot season to visit Terracotta Warriors and in the morning, there may be less people. Don’t worry about the language and there will be English service. Hope to be helpful. Wish you have a good time!