As a commencement speaker, you must do your job well. You must do it also as quick as you can. Most of your listeners are not really interested to listen to you. They want the ceremony after your speech.
I have been to many graduations where speakers after speakers seemed to love their voices too much. So far, I found that the best speakers are the students themselves. The last commencement speaker I saw delivered his speech for 45 minutes. He said “lastly” seven times.
Because many commencement speakers try to please everyone on stage, the greetings of distinguished persons waste too much time. Some speakers even tell short stories about some of them. Your speech is not about the distinguished president, but of the graduating class. If you cannot cut your long introductions, work on making it shorter, shorter, shorter, and shorter.
Be clear about your point. You must have one big idea which you believe the graduates can learn from you. Support these with three short stories. You can get the stories from your experiences and the common experiences of students.
End by painting a better future. Inspire them to own that future. Let your message be the last words from your mouth.
Deliver your commencement speech under 17 minutes. Take out all the unnecessary and you will find that seven minutes is enough to inspire and make a point.