Ysesterday, I went to heal my Pokemon team at the PC in Pokemon White and the lady at the counter said "Is today your birthday?" I put yes and she said " Happy Birthday!" I was surprised becaues it was my B-Day yesterday!!! :)
Then you clearly have the time/ date on your DS console WRONG.
P.S. Happy Belated Birthday
Go get your Happy Birthday Togekiss from Pokemon.com