24 days. Each tower is ~3 times the size of the J.L. Hudson. If these buildings were to be filled with explosives, and we assume the crews were equally competent, it would have taken over 430 people to do in the 5 days claimed by Loose change. And that is even without the worry of secrecy, which would have greatly increased the time required.
Gangsta ninja does think like a ninja. lol. if they really did it in 5 days, United States of America dedicated an entire department's worth of manpower. That will also include all security, some management, maintenance and people who work at the building in the conspiracy. If not, these people were probably equipped with futuristic alien stealth suits so that no one in that very crowded, very busy, well guarded workplace would notice them bringing in and rigging the entire building with "super hitech" explosives. Funny People indeed!