Except from what I can tell this does not happen and they pretty much start building as soon as your land is ready.
Most of the hold ups are due to us (being the purchasers) not them...
I agree with the fact they would start when your land is ready, but if you already have land that has settled and want to build with them, there is at least 3 months of activities that need to occur before you start building.
Every builder is the same, but PD make money from it.