It should be obvious that the people to whom we pitch our ideas are busy; however, when we take focus off to who we are pitching and focus on the pitch itself respect for our audience's time drops down our list of importance.
What works best for me is to acknowledge my audience's limited time for me then ask for a specific amount of time at a specific date and time. In some meetings I've brought and oven timer and let my audience set the time for our meeting.
Any successful pitch revolves around trust and respect. If your audience feels you respect their time and trusts that you will execute your commitments (more on that later) your pitches should be regularly successful.