Passing through customs in Japan is usually a hassle free and easy experience. Usually the wait to pass through customs (have your passport stamped), pick up luggage and finally get through luggage inspection takes less than an hour. However, sometimes many international flights may land at the same time and then of course it could take slightly longer. A customs officer may ask you a question or two like, "where will you be staying" or "where will you be going" (although usually they say nothing, check your passport and let you through) so just answer politely, "I am on a tour package traveling around your country to see it's great sights!" After customs you head down to pick up your luggage (usually doesn't take long) and then pass through "luggage inspection". The luggage inspector may also ask you a question and generally that's it (most people don't actually have to open their luggage... but some do). After passing through luggage inspection you are out the main passage in "in Japan!"