Much like the Calendar Man
achievement in Batman: Arkham City (Xbox 360)
, Harmonix's Dance Central 3
features an achievement that's time sensitive and can be unlocked around now (though this one is a day earlier). In fact, here it is:
The Go Shorty achievement in Dance Central 3 worth 43 pointsPerform "In Da Club" with a character on that character's birthday.
Today just so happens to be Dr. Tan's birthday, so go and pick him (if you have him unlocked!), and pick "In Da Club" by 50 Cent. Then dance through the song and this achievement will be yours!