The 2012 U.S. Open tee's off at around 10 a.m. EDT on Thursday morning with live streaming being available.
ESPN has the television broadcast the U.S. Open from 12-3 p.m. EDT with NBC taking over from 3-5 p.m., and then ESPN will finish up the day from 5-10 p.m.
USOpen.com will begin a live stream following their morning marquee group of Tiger Woods, Phil Mickelson, and Bubba Watson who tee off at 10:33 a.m. They'll also have a stream that follows an afternoon group, starting at 4:29 p.m. ET. ESPN3.com coverage will start at 12 p.m. and will have a marquee group feed, a feed for the 8th and 18th holes, and a stream that is a mirror of ESPN's television coverage.