How to Communicate your Ideas With Style, Substance, and ClarityBook - 1998
No speech should last more than 20 minutes. Why? Because Ronald Reagan said so. Reagan used to say that no one wants to sit in an audience in respectful silence for longer than that, if that. He knew 20 minutes was more than enough time to say the biggest, most important thing in the world. The Gettysburg Address went five minutes, the Sermon on the Mount probably the same.
Some communications professionals will tell you there are specific gestures to use when you make a speech, particular ways to move your hands or use your voice. I do not think this counsel helpful. Be yourself in your presentation, because although there have already been Vince Lombardis and Dan Rathers and Jesse Jacksons, there has never been a you before. So you might as well be you and have a good time. Authenticity isn't just half the battle, it's a real achievement."