Sale of investment property joint ownership

I purchased a home with my father in law in 2015.  He was considered a 1% owner and I was a 99% owner.  He has since lived in the home and paid "rent".  Technically, the property is listed as a rental property on my taxes.  If I were to transfer ownership to him, how long would he have to wait before he could sell the home and be eligible for the exemption?  He has never owned/sold a home before.

 

Thanks in advance for any assistance.