The main terminal is quite straight forward, one long building with services (transfer desk, aerotrain platform, lifts, escalators etc) in the middle. Before you get 'down' to the immigration level, there is a transfer / info desk where they can give you the precise directions. Even if you miss it, I don't think there is much of a queue at the main immigration counters given your time of arrival but you will be making a long loop to the domestic departure hall.