From the National Moment of Remembrance website (www.remember.gov):
The National Moment of Remembrance, established by Congress, asks Americans wherever they are at 3 p.m., local time, on Memorial Day to pause in an act of national unity (duration: one minute).The time 3 p.m. was chosen because it is the time when most Americans are enjoying their freedoms on the national holiday. The Moment does not replace traditional Memorial Day events; rather it is an act of national unity in which all Americans, alone or with family and friends, honor those who died for our freedom. It will help to reclaim Memorial Day as the sacred and noble holiday it was meant to be. In this shared remembrance, we connect as Americans.