section 54F

Hi,
My uncle sold a non residential property last financial year and purchased residential property and he was eligible for 54F exemption
Now, is there blockin period to retain the above new property.

suppose if he sells the newly acquired residential property and purchase another residential property, what would be the tax impact, will the above claimed section 54F will be revoked.
the tax assessment for last year will be done only by September 2019

please guide
kiran