New Construction Tax Timelines

[Trenton Parks]

Had a quick question for those that do new construction.  

Do taxes for new construction in regards to 1031 exchanges and the 2 year rule, start when the home is completed or when you purchase the lot and begin construction?  This would also have big impact on long term vs short term gains since most construction takes 6-9 months to complete.

Thanks in advance to the tax experts out there.