e. When the time box expires
All the Sprint activities are time boxed including Sprint. Unlike other Sprint activities, Sprint can neither be extended nor shortened.
If for instance, all the items of a Sprint are not completed, the Sprint is still marked over and the remaining item(s) is moved to the Product Backlog from where it can be scheduled to any of the subsequent sprint based on the revised priority. Similarly, the Sprint can never be shortened.
If all the Sprint items are completed before time, the development team is free to pull in the top Product Backlog items and start the development.