The time is misstated in this article. The 911 call came in at 12:13. All other articles say the boys arrived "about noon". Also, the e-mails went out at about 12:05. I think that was timed to happen after the plan was put in action.
Just adding:
After 10 minutes of pounding on the door, G-H placed a frantic call to 911, saying she was locked out, one of the boys was crying and she smelled gasoline.
http://www.sltrib.com/sltrib/news/53473091-78/call-powell-dispatcher-information.html.csp