As A_Lee suggests, it's very hard. If you need to make Westin chosun by 9am, consider arriving Seoul one day before. ICN is a massive, inefficient airport, especially for concourse A arrivals. Slow escalators, infrequent trains (only every 5 mins from concourse to main terminal; twice more on the other way, though), walking and walking. Taking train to Seoul will add another 10-minute just for walking + escalators, so bus is better most of the time.