Sprints are invariant durations of time. The longest sprint duration that Scrum allows is 4 weeks. To be honest, I feel that a 4 week sprint is far too long before providing feedback to the Product Owner. The shortest Sprint duration is 1 week. Most teams have a Sprint duration that’s either 2 weeks or 3 weeks long. I personally prefer a 2 week sprint because I feel it’s a nice balance between providing regular feedback to the Product Owner, and is still long enough for the team to actually deliver some increment of potentially shippable product. Everything in Scrum happens within the duration of a Sprint, and we the repeat the Scrum framework Sprint-over-sprint-over-sprint.
Sprint durations are decided at the start of a project, and once decide the sprint duration remains unchanged. For example, we don’t do a 3 week sprint followed by a 1 week sprint. If we’re working with a 3 week sprint, then its always 3 weeks long.
In a similar fashion, we never extend the sprint by a few days, nor do we shorten the sprint by a few days. So, here are two question for you to consider. If the team finishes all their work two days before the end of a sprint, what should they do? If the team requires just two more days to complete their work, what should they do?