It happens around the three-minute mark. *Chills*
From the video's description:
At 1:45 a.m., Campaign Manager Richard Carlbom of Minnesotans United for All Families announced to campaign staff and board members that the vote on the proposed constitutional amendment to ban same-sex marriage in Minnesota was too close to call. As he was about to end his remarks and tell everyone to get some sleep, Carlbom was told by the campaign's communications director Kelly Schwinghammer, "The AP just called it." An impromptu, joyous, tear-filled celebration ensued. It was the first time in U.S. history that an anti-gay marriage constitutional amendment had been defeated.
Source: youtube.com
