Personal communication from a highly reliable source:
The First Sister will be ready for occupancy by September of this year. By the time this happens, the Second Sister will already be topped off, and the tower crane will have been moved to allow construction of the Third Sister.
The rapidity of construction of this massive project is staggering, certainly much quicker than other smaller construction sites around the city.
It actually makes sense to have the Second Sister topped off and the crane moved by September. The recessed courtyard and traffic turnaround in front of the complex will have to be clear in order to make the building fully functional. This means a paved driveway and completed landscaping too.