Opportunity Zones - Is There a Window for Reinvesting?

[Mindy Jensen]

I just heard of this thing called Opportunity Zones. A guy I met recently has sold his rentals this year, and is getting ready to take a tax hit. I don't know enough about Opportunity Zones to speak intelligently about them, so I told him that they exist, and sent him on his researching way.

Are OZ's an option for him or is it more like a 1031 where there is a limited time window? 

Tagging @Jay Hinrichs because he knows everything.