This can be different from builder to builder. It also depends if the builder is a developer or just buys developed lots. It also can depend on cash flow and their specific business plan.
At my previous job, we were developers and builders. At one time we had over 150 lots developed, and another 60 acres or more that we owned but hadn't developed yet.
Me personally, just starting out, I just bought 3 lots here adjacent to one another. I close on them in a couple of weeks and will be able to start immediately. My homes will be spec, and I will stagger the start of them (30-60 days apart), when the first one goes under contract, I will purchase another lot. My goal is to always have a home ready to buy, I may need to increase to 4-6 lots in order to do so, we'll see how 2015 rides out.
In my Town it takes 2 weeks or less to get building permits, maybe it helps that I sit on the Planning and Zoning Board, but we are a small beach town. Permits to create a subdivision is a whole other ball game, 6-12mos depending on the size/scope.