There are many new home developments. When a development is built, usually the home builders, such as Pardee, America West, etc. can often sell the property before it is built. There can be many delays which could explain the difference in time.
On one property I built in California, I had an Occupancy Certificate from the building department, which certified my construction was final. It took nearly 6 months for the county to record this document.
If anyone is interested in a newer home near Summerlin Parkway and the 215 please click on my Virtual Tour link. This house is a gorgeous 3 bedroom with large den/study downstairs which can easily be turned into a 4th bedroom There is also a spacious loft upstairs for a gameroom or playroom. The floorplan is open and flows. Enjoy your beautiful yard with grass for the kids to play. Striking Mountain Views and parks nearby.