When asked to speak at the podium for 20-minutes, do you actually have 20-minutes of good material you can use?
It’s the same for musicians, comedians, magicians, anyone who wants to perform needs a good set.
Your job is to change someone’s emotions. Every minute on stage is precious. Don’t waste their attention by stretching your time slot.
People are there to see a good show. Not a mediocre one.