Obviously it had to have been sometime before The Last was marketed but....it definitely wasn't halfway through the series like Kishi claimed (When Sasuke was gatehring around Taka)
Because we had the whole Sakura calling for Naruto during teh Pain fight, the hug, the Tales of teh Gutsy Ninja where Sakura actually marries Naruto, Kushina's final request, Minato giving NS his blessing. The NS/SK parallel in 662, CPR, Kakashi flat out saying that Sakura doesn't love Sasuke anymore and again in 293 when she says that her desire to save him is purely platonic and "she doesn't want to be yours"