Every day at 5:00 a little song is played over loudspeakers in Tokyo. I have heard that the song is different in different areas, but where I live this is the song I hear every day reminding me to come home from the rice fields for dinner.
About a week ago the annual Illumination lights were set up in my neighborhood as well. And they come on at 5PM also. What I mean is they come on exactly at 5PM when the chime starts playing. These two systems aren't linked in any way -- it might be something as simple as a person hitting the switch when they hear the chimes playing for all I know. When I first moved here I used to watch a GPS-synced clock and it was uncanny to watch the 4 change to a 5 exactly when the first note of the song played.
Japanese people are very precise about time, so of course the lights come on exactly at 5PM. In fact it would seem quite strange if the lights were delayed by even a second or two. It's one of the cool little unique things that makes life interesting here.