"Once the HIV-infected partner is fully suppressed we observed no infections, none. So the critical period is the first six months of treatment."

They recommend condom and PrEP as a "bridge" before and during ART start up.

http://www.thebodypro.com/content/75595/hiv-transmission-risk-remains-during-first-6-month.html?ic=700102

I think it should be 6 months AND an clinical Undetectable viral load. Some people can take 8 months to a year to reach their undetectable status.