My experiences to KIX every year reaching on the morning/noon flights has always been long queues, so I would stay give it around 30 mins to 1 hour. Even though the queues are long, it seems to move at a steady pace.

Remember to fill in your arrival card as well. If you are a US Citizen and have US Global Entry, you can apply for Japan's Trust Traveler's Program (TTP) which gives you access to automated gates which can be used at some of the major airports in Japan (free service).

Unfortunately for the rest of us folks, it will be very difficult to get unless you somehow have working relationships with Japan.