Four years ago, SM (Entertainment) told Taemin to use “I’m Crying” (Korean version) as the title track for the album 'MOVE-ing' because of a lack of time to prepare.  Taemin, however, had other plans as he co-composed and wrote the lyrics to “Day and Night.”  Taemin also created the choreography in a short timeframe so that he would have a title track with the performance ready to go.  

Just as Taemin wanted, MOVE-ing - The 2nd Album Repackage would have the title track - Day and Night, along with an instrumental version; and three other songs - Snow Flower, I’m Crying, and Hypnosis.   Along with these four new songs, the full album would have 13 songs in total. The digital release was on December 10, 2017, and the physical album was released the next day.
 

Why did Taemin go to so much trouble? As aptly described by a fan from Twitter: “One of the things we appreciate most about TAEMIN is the genuine love for his fans. He co-composed & choreographed this song in record time so that fans would have something new for MOVE-ing”. — Source: @streamfortaemin (Twitter).

Above we have the SMTOWN MV of “Day and Night,” and below is the MUSIC BANK (KBS KPOP) stage performance. Both were released on December 8, 2017. 

Taemin would go on to perform this beautifully put-together song with choreography on other music shows, including the one below. 

Happy 4th anniversary to "Day and Night!"