Today is equinox, at which the daytime and the night take equal time. As the sun is already going down now, I might say today was it.
In Japan there are no special festival for summer or winter solstices like what I have heard about scandinavian area, instead, spring and autumn equinoxes are national holidays.
Why Japanese are so pleased to have equal length of day and night?
As a matter fact, it is not the reason.
Traditionally, these two have been the days when people visit graves of their ancestors, pray for them, and set flowers, fruits, or a special kind of sweets in front of the gravestones.
( Nowadays people don’t set foods outside, because they would be perished and cause crows or insects to wander )
Why are these days so special?
The Japanese explanation on equinox in Wikipedia would give a good hint.
According to it, the important feature of equinox is that the sun goes down exactly in the west. In ancient Japan people believed the paradise lie in the far west. So if you see the sun going down, you could see the paradise, where the ancestors live.
Of cource, people pray for recent members of the family who are dead. So the two equinox days this year must have been filled with much deeper prayer than usual.