Yeap, looks like it's for real. I'm all for having a 日 for ファン to celebrate the 本 and/or JK Rowling, but 7 分 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 もっと見る Harry Potter related should have been picked to do on the day. I like how ファン of Douglas Adams have Towel 日 - where ファン are encouraged to carry a towel with them on the 25 of May, because according to the Hitchiker 本 a towel "is about the most massively useful thing an interstellar hitchhiker can have."