IT has a transfer desk too, at the international arrivals, after baggage claim and customs. The transit bus goes to the domestic terminal airside, but will drop you off cityside, which means you need to pass through the airport entry gates like any other pax would. Agree, they don't normally let in people too early, but a bit of pleading and a nice guard normally ensure you can get into the terminal building. IF that happens, you can then always use the lounge to relax. It might be better for you to book a room at one of the hundred odd hotels close to the airport, but with your given timings of arrival and departure, you may think later on that the overnight stay wasn't worth it. But what the heck, at least that way, you get to sleep !