Not really. The 9/11 hijackers didn't sit around for years waiting for a secret signal from OBL. Rather, they were basically on their own and it was up to them to decide when to make their move. They weren't trying to blend in to the American populace for years until the time was right. Rather, they single-mindedly went forward with their plan and executed it more or less as soon as they were ready.
The monsters have patience that most Americans can't even comprehend.
19 guys spread around the country planning an attack is one thing. If they're smart, there is very little to draw the attention of the authorities.
A bunch of guys sitting on a nuke is quite different. The longer they wait, the more likely something is to go wrong.
Not a secret signal. The orders were given to Atta, who carried the message to cells already in place in the United States.
If you believe that the date was just randomly chosen by some semi-freelance terrorists, do you also believe that the 9/9/01 assassination of General Ahmed Shah Massoud (leader of the Northern Alliance) was a coincidence?