According to this it was 4:25:
When Desiree Young's phone rang at
4:25 p.m. on June 4, she answered, not knowing the call would forever change her life.
Susan Hall, the secretary at Skyline School, was calling Young because she was listed as
an emergency contact for Young's son, second-grader Kyron Horman.
"She told me, 'I need to notify you that he's missing,' and I said, 'What?'" Young recalled in an interview with The Oregonian. "She said, 'He's missing.'
And I said, 'I don't understand what you mean, he's missing. How can he be missing?' And she said, 'I'm sorry,
they asked for me to call you.'"
http://www.oregonlive.com/portland/index.ssf/2010/07/kyron_hormans_mother_recalls_d.html