I had a modular home built. Still took 6 months.
What was the delay? I was looking into them and read that it took two to three Months. I would assume it depended on whether the Factory not having a backlog of Orders.
Of course this also depended on already owning the Land and the availability of Water and Power.
There is something to be said about having the Home Constructed in a protected environment, rather than being exposed to the Elements.