Possibilities:
1. Feds are conducting covert tests to determine response times;
2. Terrorists are conducting tests to determine response times;
3. April fools prank.
In any case, the media is being rather too helpful, don't you think?
"discovered on April 1 at 9:40 AM..."
1. I don't think the Feds left the suitcases.
2. The K-9 guys saw a pattern, a statistical change in the routine; the question is whether this change resulted from a single cause, or multiple causes. If it was a single cause, the most dangerous possibility, if not the most likely, would be a practice/training operation for planting bombs by some terrorists.
The main waiting room in Penn Station is very big and crowded; and guess what, I recall that Penn Station is real close to Madison Square Garden, where the Convention is to be held. Certainly within "kiloton" range of the Garden, as it were.
3. This would be a rather lame April fool's prank. Now, it would be funnier planting the suitcases and then calling the Port Authority, reporting a lost suitcase, having them retrieve all these suitcases and you say, "no, that's not mine." After about the tenth one, go home and send them an April Fool's card, ha ha ha.
The media are giving the response time to any terrorist who knows when the suitcases were planted, assuming that the time given was not changed. This is certainly a concern for more than one reason. Can the City shut down Penn Station during the Convention?