Anecdote on how fast you really can build a house
It is all about scheduling and handling your manpower.
In 2008 Lennar Homes was building a tract in Lytle Creek in Southern California. Tract builders always complete model homes first so they can start selling them.
They had 3 model homes to build, nice quality, with fireplaces and kitchen islands etc. each home over 2000 square feet. They pushed the subs as always with models. the record was set by a Jenike brother who was superintendant he had the previous set of models done in 30 days.
Another Jenike brother was in charge of this job. He wanted to beat his brothers record.
YES, they got three homes built, completely and ready to move furniture in in 28 days.
It isn't impossible. We have seen it done.