how long does it take to go from Xian Airport to the North Railway Station

Hi, Please let me know above, and also do you have a direct bus between the airport and the North Railway Station (and vice versa). Also what time does this service begin in the morning.
I will arrive at XA North Railway by the first 'bullet train' at about 8.50am, i need to rush to airport to catch my 11.00am plane. What is the best mean for me & how much will this be? Thank you.