No one ever complained about a PowerPoint presentation being too short. The second an audience gets bored and stops paying attention, the presentation loses its effectiveness. People not only stop processing new information, in fact, but begin to resent the presenter for wasting their time. So Kawasaki, for example, thinks that an ideal PowerPoint presentation should last no longer than 20 minutes.
That leaves time for a question-and-answer portion during a 30- or 60-minute meeting and ensures you make the most of people's time. When planning the narrative that will accompany your presentation, make sure your key points are honed. You may decide to ditch less important points altogether.