With 220 floors and 104 elevators...that's more than 2 floors and 1 elevator a day. I imagine just the fitting/assembling in place process per floor is enough to fill up a third of a day on its own...so is this basically a huge vertical jigsaw puzzle in which the pieces have been made and just need to be moved onto site?
So one way this headline could be strictly true is if all of the floors of the building were fabricated off site, once they were ready the company might be able to assemble the final building, in a prepared foundation, in 90 days. That is the only interpretation I can think of that works.
Concrete can take 4 weeks to get to 90% strength [1], so if you didn't do the prefab route you would have to spend more than 90 days just waiting for the lower levels to cure so that you could build the upper levels.
I am interested in what they are trying to do though, it sounds like an interesting challenge.
Concrete made with Type III portland cement achieves most of its strength within seven days (concrete made with normal (Type I) cement reaches its design strength in 28 days).
When one needs significant strength more quickly, the mix can be adjusted to provide a higher ultimate strength than is required for the intended loads during the normal life of the building and accelerants added . This results in adequate capacity for construction to continue in as little as a few hours.
Conversely, prefabricated units can be built virtually anywhere and shipped economically over long distances...i.e. fabrication can occur at a factory in a rural location and assemblies can be moved by rail or barge.
http://www.nytimes.com/2011/06/26/business/global/26bridge.h...
What made it practical was the specifics of LIHTC funding. A significant amount of the funds had to be spent upfront on materials and/or labor or it would have been lost. This made the long lead time beneficial because early stages of construction such as clearing and grubbing are relatively inexpensive whereas finishes are relatively expensive.