Even false memes spread fast
I receive quite a bit of traffic today from Yahoo! search on "911 days madrid bomb" and similar terms. I earlier pointed out 3/11-04 was 912 days after 9/11-01. I assume if this had been important for the terrorists, they would have attacked the day before.
I doubt, however, that it was a coincidence it occurred two years and six months after the WTS attacks. But date magic has not been a characteristic of al-Qaeda. It would, however, fit domestic terrorists wanting to blame Islamists for political reasons.