The responsibility of time boxing (or limiting the amount of time spent) in a Scrum meeting is given to the ScrumMaster. He maintains a time-box so that the Scrum Team will become more and more effective in how they use the time to its full purpose. We, as human beings, thrive in situations where we have simple constraints and focused goals – time-boxing of Scrum meetings fits this perfectly. If a Scrum Planning meeting, for example, is not time-boxed it can become disconnected from the goal of the Scrum Team. Time-boxing also helps Team Members to be engaged, since they have a limited amount of time to achieve the goal of the meeting – such as a Sprint Goal that is generated from the Sprint Planning meeting.
To learn more about how you can improve your Scrum meetings, visit the Scrum Team Assessment.