June 17, 2019 3:20 PM
I know you would like to see chapter and verse from the IRS code but not sure it is spelled out.
Here is a web article from a company the facilitates 1031 transactions. It suggests two years will satisfy the 1031 guidelines.
Disclaimer: Not a tax professional. Information gathered from internet links. Anything dated in June 2019 was posted in prior years and is before the 2019 limits and changes.