As a 'timekeeper' a drummer who ensures that the speakers (guaranteed) keep to their allocated time.

Obviously in agreement with everyone including the speakers, the drummer comes up the last five minutes before the end time of each speaker and very gently eg with the drum brushes he / she gives the signal that the end time is approaching.

As the last 5 minutes progress, the drumming gets louder and louder until the speakers can only stop. Believe us, your total event ends on time!