There’s a special word in Japanese for “Cherry blossoms at night” – yozakura (夜桜). According to this announcement published on the Kumamoto JET website, starting tonight, the castle grounds will be open until 9 PM so that people can continue to enjoy the blossoms after the sun has set. I’ve read, however, that the blossoms are not predicted to start popping until the 23rd or so.
https://kumanichi.com/news/local/main/20160318002.xhtml
http://kumamotojet.com/shin/index.php/2016/03/18/night-cherry-blossom-viewing-at-kumamoto-castle/