In the Old Testament, various unscrupulous gentiles would wait until the Sabbath -- the Jєωιѕн day of rest -- to attack Israel. They used the Sabbath rest against the Jєωs.
Fast forward to today.
Throughout Lent, many pious Catholics are going to be doing extra prayers, penance, good works, spiritual reading, etc. and many will be spending less time on the Internet/message boards/CathInfo/etc.
What better time for "something to happen" than during Lent, when the greatest number of Catholics are "distracted" with their souls and eternal salvation?
If they want the element of surprise, they certainly won't find a better time throughout the entire year.