Expect a few flights arriving around the same time as your arrival, since most flights leave Tokyo at the same time. That being said Singapore Immigration is usually quick and professional.
A nice, sweet touch is a bowl of hard candies on the Immigration Officer's counter meant for the visitor. Bags arrive quickly and the city is a fast taxi or shuttle ride from the airport. Singapore's rapid transit system closes before the late bank of arrivals.
Overall, Singapore arrivals are pretty quick, civilized and effortless which is a blessing after a transpac.