Yeap, looks like it's for real. I'm all for having a día for fans to celebrate the libros and/or JK Rowling, but 7 minutos of silence?!! I agree with cassie-1-2-3's link on that one: it's disrespectful towards real victims of tragedies and wars.
Something a bit más Harry Potter related should have been picked to do on the day. I like how fans of Douglas Adams have Towel día - where fans are encouraged to carry a towel with them on the 25 of May, because according to the Hitchiker libros a towel "is about the most massively useful thing an interstellar hitchhiker can have."