you get 51 days from Tisha b’Ov thru Rosh haShono.
Should we commemorate 9/11 Absolutely!! I wore my WTC this past Thursday, and shall be wearing it again this coming Thursday. I personally witnessed the 2nd plane ram into the 2nd WTC, and simply cannot get this horrifying image out of my mind.
I recently was at Flight 93 Memorial in Shanksville PA, and it alos left a profound mark on me, having visited this sight.