Stakeholders will change their minds on requirements, and as the Agile value reads, "Responding to changes over following a Plan", we should allow the methodology to accept these changes regularly.
The Sprint Review is an avenue for the Scrum team, including the Product Owner, to receive feedback on the Product Increment they have developed in the Sprint.
Who - The development team, Scrum Master, and product owner. Key stakeholders such as management and maybe even key customers should attend to provide feedback.
When - At the end of a Sprint when the Product Increment is completed, but before the Sprint Retrospective.
Length - One hour per week of work. Sprint Review should take approximately two hours if Sprints commonly occur over two weeks.
Flow - The goal of this event is to receive feedback on Sprint's Product Increment. The Scrum Master or Product Owner organizes the meeting, showcases the team's completed work, and facilitates questions from stakeholders and customers.
Outcome - Input for upcoming Sprint Goal and changes to the Product Backlog due to re-prioritization or additions.